Gregor Clegane

Ser Gregor Clegane was a knight of House Clegane, the older brother of Sandor Clegane, and a notoriously fearsome, extremely lethal and much-feared warrior, with a tendency toward extreme and excessive violence. Due to his incredibly massive size, he is called "The Mountain That Rides" or more often simply "The Mountain."

Background
Ser Gregor Clegane was the head of House Clegane, a knightly house from the Westerlands, and the elder brother of Sandor Clegane. When Sandor and Gregor were children, Gregor held his brother's face in a fire for playing with one of his toys without permission, horrifically scarring him. Gregor was a landed knight rather than a full-fledged lord. Gregor was monstrously huge, said to be the largest, strongest and most feared man in Westeros. He was feared throughout Westeros with a reputation for ferocity, brutality and anger. It was believed he has committed unspeakable acts of violence, such as brutally torturing his victims to death, raping women and murdering children. He was a fiercely loyal retainer and servant of House Lannister, particularly to Lord Tywin.

Numerous servants have gone missing at the Clegane keep over the years, apparently killed by Gregor for minor slights in one of his infamous fits of rage, and their deaths then covered up. Gregor's own father and sister died under dubious circumstances as well, and Sandor thinks that Gregor may have killed them as well. Their sister died when Sandor was too young to remember her well, and their father died years later in what was said to be a "hunting accident". At the request of Tywin Lannister, Prince Rhaegar Targaryen himself anointed Gregor as a knight, a great honor, even though Gregor was an infamously dishonorable man.

During Robert's Rebellion, one year after Prince Rhaegar knighted him, Gregor participated in the Sack of King's Landing. After entering the Red Keep he viciously killed Rhaegar's two children by Elia Martell: their daughter Rhaenys and baby Aegon. He killed baby Aegon by bashing his head against the wall, and then while still covered in the gore from her children proceeded to viciously rape Elia, after which he killed her. It is rumored that he killed her by cutting her in half with a single swing of his massive sword, although he later claimed to have "smashed her head in".

Despite pleas by Ned Stark, neither Gregor nor Tywin were punished by King Robert for the murders of the royal family, leading to a rift in Ned and Robert's friendship.

Season 1
Ser Gregor takes part in the tournament to celebrate Eddard Stark's appointment as Hand of the King. He kills Ser Hugh of the Vale in a joust, horrifying the crowd. Littlefinger tells Sansa Stark that Gregor burned his brother Sandor's face over a naked flame when they were boys because Sandor borrowed one of his toys without asking. He tells her that few people know the story and not to let Sandor Clegane know that she does. When Gregor faces Ser Loras Tyrell, he loses the joust because Loras chose to ride a mare that was in heat to distract Gregor's stallion. Flying into a rage, Gregor demands his sword, then ruthlessly decapitates his erstwhile mount before the entire horrified crowd. Ignoring his surroundings, he continues to knock the surprised Loras off his horse, and is on the verge of dishonorably killing him, when his brother Sandor intervenes, fighting him off to protect Loras. The two brothers violently trade swings with their swords, and Gregor only stops when King Robert himself shouts to stop the fight, at which the enraged Ser Gregor stops and leaves.

Catelyn Stark takes Tyrion Lannister into custody on suspicion of the attempted assassination of her son Bran. In response Gregor was dispatched to raid the Riverlands, her homeland. Refugees from the Riverlands attend court in King's Landing and report that a huge knight who could take the head of a horse in one blow led the attack and had sacked their villages. Littlefinger asks "Remind you of someone?" Eddard Stark sends Ser Beric Dondarrion with a hundred men to bring Gregor to justice. Eddard declares him a false knight and strips him of all ranks and titles, lands and holdings, and sentences him to death. The ruling was made null by Eddard's arrest for treason and subsequent beheading.

The host led by Lord Beric clashes against Ser Gregor at the Mummer's Ford. Ser Gregor is victorious, and Lord Beric is reported dead.

However, when Robb Stark's victory against Jaime Lannister forces Lord Tywin to withdraw his forces to Harrenhal, he orders Ser Gregor to take five hundred men and "set the Riverlands on fire" from the Gods Eye to the Red Fork.

Season 2
Gregor continued to raid the villages of the Riverlands from the Lannister army's base at Harrenhal. His men tortured the prisoners they take for information about the Brotherhood and hidden valuables. He selected the prisoners for torture personally. Ser Amory Lorch adds a group of captured Night's Watch recruits to the captives. Lord Tywin Lannister arrives during the torture and asks Gregor what is going on. Gregor sayid that they were not expecting Tywin for another day. Tywin asks why the prisoners are not in their cells. Gregor says that their cells are overflowing. One of Lorch's men interjects that the prisoners will not be there long. Tywin asks if they are so well manned that they can afford to discard able and skilled prisoners. He asks a prisoner if he has a trade and learns that he is a smith. Tywin orders the prisoners put to work, sparing the young man.

When the Ironborn under the command of Theon Greyjoy attack Torrhen’s Square, to lure the remaining Stark forces away from Winterfell, Ser Rodrik Cassel assumes that it could be a raiding party led by Ser Gregor. Following the assassination of Ser Amory just outside Lord Tywin's chamber, Ser Gregor was tasked with finding the culprit. Tywin fears that he was the intended target and has Ser Gregor hang over 30 of their own men. Ser Gregor suggested an infiltrator from the Brotherhood Without Banners was responsible and Lord Tywin dispatched him to pressure the smallfolk of the Riverlands into giving up the members of the Brotherhood. Tywin marched back to the Westerlands and left Gregor to serve as castellan at Harrenhal.

Season 3
Robb Stark and his army get to Harrenhal, finding that Gregor Clegane has left the castle with his men. To their horror, they discover that Ser Gregor has executed the remaining 200 Northmen and Rivermen prisoners at Harrenhal, leaving their bodies to rot.

Ser Gregor was later expelled from Stone Mill by a force led by Robb's uncle, Lord Edmure Tully, forcing him to flee south to Casterly Rock. However, Robb chides his uncle for his actions, explaining that he wanted to draw the Mountain into the west where they could kill him.

Season 4
Oberyn Martell discusses with Tyrion how the last time he was in King's Landing, it was for the wedding of his sister Elia to Rhaegar Targaryen. He also states that during the Sack of King's Landing, his sister was raped and murdered by Gregor. Oberyn believes that Tyrion's father, Tywin, was the one to give the order to the Mountain. He told Tyrion that he intended to avenge her. ​Polliver tells Gregor's brother when meeting in a tavern further north, that while loyal to the Mountain and the Lannisters, Polliver wasn't in agreement with Gregor's torturous methods because they were repetitive and boring. When Tyrion demands a trial by combat, Gregor was quickly appointed the Crown's champion by Queen Cersei Lannister in order to deter anyone from fighting for Tyrion. Tyrion first asks his brother Jaime to fight for him, but he declines, saying that he simply cannot fight like he used to with the loss of his sword hand. Tyrion then asks his friend Bronn to be his champion, but he too refuses, arguing that the Mountain was an incredibly dangerous fighter, one that would cost him his life if he makes a single mistake. Finally, Prince Oberyn Martell approaches Tyrion and volunteered to be his champion, as he wants to avenge his sister.

Gregor fought Oberyn at Tyrion's trial by combat, clad in a heavy plated armor and wielding a large broad sword with one arm. Despite his immense size and strength, Gregor is no match for Oberyn's swift and agile fighting style. Oberyn managed to knock Gregor's helmet off early into the duel and proceeds ​to slowly cut him down, all the while taunting him and demanding he admit to the rape and murder of Elia Martell and her children, chanting ever more loudly "you raped her; you murdered her; you killed her children". Oberyn eventually severs ​Clegane's hamstring, causing him to fall to his knees. Oberyn presses his advantage by jumping and thrusting his spear into Gregor's chest, severely injuring the gigantic man and seemingly sealing his defeat. Thinking his opponent is fully incapacitated, Oberyn removes his spear from Gregor's chest and circles him, refusing to land a killing blow until Gregor admits that he killed Elia and reveals who orchestrated it, directing his gaze accusingly at Tywin.

However, in his hubris, Oberyn is unexpectedly caught off guard when Gregor trips and pulls him to the ground, grasping him around the neck and slamming his fist squarely into his face, instantly knocking out several of his teeth. Berserk with fury at nearly being killed by his opponent, Gregor pins Oberyn to the ground and proceeds to gouge out his eyeballs, making him scream in agony, as he roars for all to hear: "Elia Martell! I killed her children! Then I raped her! Then I smashed her head... in like this!". He then crushed Oberyn's skull, making his paramour Ellaria Sand scream in horror. Gregor collapses beside his fallen opponent from the wounds he sustained as Tywin announces that, according to the rules of trial by combat, Oberyn's death has officially sealed the fate of Tyrion Lannister and sentences him to death.

Despite his exceedingly gruesome death, Oberyn nonetheless manages to get some posthumous revenge. Before the duel, Oberyn had his spears coated with manticore venom, one of the deadliest poisons in the known world. The venom causes Gregor's wounds to start putrefying, emitting an overpowering stench. As a final torture, the venom forces him to remain conscious during the whole ordeal, even with dead flesh hanging off of him. Grand Maester Pycelle regretfully told Queen Cersei that Ser Gregor is beyond any hope of healing. Qyburn, however, an expelled former maester with extensive medical knowledge gained from "repugnant" and "unnatural" experimentation on living people, suggests that he may be able to save him. Cersei dismisses Pycelle and gives Qyburn permission to do anything he can to save Ser Gregor (likely out of gratitude for sealing Tyrion's fate and her 'revenge' on him for the death of Joffrey), though Qyburn says that his unorthodox methods may "change" him. She nervously asks if he means the process will weaken Gregor, but Qyburn knowingly assures her it will not.

Season 5
A moribund Gregor Clegane is being experimented on by Qyburn at his laboratory in the dungeons below the Red Keep. Queen Cersei visits Qyburn and asks him about the state of his work, while glancing at Gregor's covered body, and Qyburn assures her it is going very well, though there is still a way to go. Then, Gregor suddenly spasms, and Qyburn gently shushes him and tells him to go easy. During Cersei's imprisonment by the Faith, Qyburn reminds her that "the work continues."

After Cersei's walk of atonement, she returns to the Keep where Qyburn covers her up and is pleased to introduce the "newest member" of the Kingsguard. The Mountain stands as tall as ever, fully covered in Kingsguard plate armor. Only his reddened eyes, surrounded by pale blueish flesh, are visible through his helmet. With Cersei's feet injured and bleeding, he is instructed to carry her. As he does so, Qyburn informs Cersei that Clegane has taken a holy vow of silence to last until all of Tommen's enemies are dead and the evil has been driven from the realm.

Season 6
Gregor is present standing guard over Cersei when Jaime returns with their daughter's body. Later, Gregor continues to serve Cersei without question. He fiund a man who boasts of having flashed his penis at Cersei during her walk and bashed his head against a wall, killing him.

Back at the Red Keep, he accompaned Cersei when she attempts to attend Myrcella's funeral, only to be stopped by a group of Lannister soldiers, who have arrived to prevent her from leaving on King Tommen's orders. Although Gregor intimidates the captain with his size, Cersei acquiesces, and he escorts her back to her room.

Gregor follows Cersei and Jaime into Qyburn's laboratory, where the former Maester was trying to win the service of the Little Birds by offering them candied plums from Dorne; the children are extremely frightened by the towering knight and quickly flee the room. Jaime asks what Qyburn has done to Gregor, to which the latter replies with "a number of things". Jaime wonders whether Gregor is able to understand complete sentences, to which the huge knight menacingly turns his head towards Jaime. Qyburn assures that Gregor understands well enough. Jaime suggested sending Ser Gregor to the High Septon to crush him and his Faith Militants. Cersei disagrees, saying they can't let Ser Gregor face them all and that he only needs to face one, implying the coming Trial by Combat. At the Small Council, Pycelle expresses his disgusts about Qyburn's treatment of Ser Gregor, calling him an abomination. He attempts to suggest that it would be in everyone's best interest to have the "beast" destroyed, but he was cut short when he becomes aware of the presence of Cersei, Jaime and Gregor himself. Frightened by the huge man in shining armor, Pycelle cannot keep himself from passing gas. Kevan argues that Cersei and Jaime have no position on the Small Council, but Jaime replies by saying the Lord Commander of the Kingsguard has. Cersei suggests the Small Council gets on with urgent matters, as they cannot make them leave. Kevan replies that Cersei and Jaime cannot make them stay either, unless they set Gregor to kill them. As everyone except Cersei and Jaime leave, Pycelle cowers past Ser Gregor, who coldly looks back.

After Cersei got word of Olenna Tyrell's intention to return to Highgarden, she confronts her. Ser Gregor Clegane follows in the Queen Mother's wake and silently stands guard behind her.

When Lancel and several other members of the Faith Militant enter the Red Keep, Cersei, Qyburn and Ser Gregor arrive to confront them. Lancel tells Cersei that the High Septon wishes to speak with her, but Cersei refuses, and when Lancel does not leave at her command, Gregor stands in his way as the Faith attempt to forcibly take Cersei. He remained unmoved when Lancel orders him to stand down. One of the Sparrows attacked Gregor, and although his weapon's spikes pierce Gregor's plate, Gregor does not say a word or appear to even acknowledge any injury. When the Sparrow tries to attack again, Gregor grabbed him by the throat, lifting him into the air and throwing him to the ground. While Lancel and the other Sparrows look on in horror, the towering knight kneels beside him and tears his head off. Lancel and the others thereby stand down.

Ser Gregor accompanied Cersei and Qyburn to the Great Hall, where Tommen is about to make a royal announcement. As Cersei attempts to stand besides her son, she is barred by Kevan Lannister, who tells her place is on the gallery with the other ladies of the court. Cersei reluctantly takes her place there with Gregor following her, causing the women to hastily make place. Tommen announces that Cersei and Loras Tyrell will stand trial before seven Septons and that trial by combat is forbidden in the Seven Kingdoms, thereby nullifying Cersei's plans on having The Mountain fight as her champion again. On the day of her and Loras Tyrell's trial, Cersei sends Ser Gregor to Tommen's chambers, to prevent him from going to the Great Sept of Baelor to protect him from its destruction. Tommen tries to get past but Gregor easily holds him back. Tommen later commits suicide after hearing of Margaery Tyrell's death in the destruction of the Great Sept of Baelor. Ser Gregor is summoned by Queen Cersei to the Red Keep dungeons after the explosion, being introduced to Cersei's newest prisoner, Septa Unella. After removing his helmet, revealing his withered and mangled face, Gregor is left alone with Unella, who screams in terror as The Mountain looms over her, ready to carry out his orders to torture the Septa for imprisoning and humiliating Cersei.

Later, when Cersei is crowned as Queen, he is seen looming beside the Iron Throne, gazing into the crowd.

Season 7
Ser Gregor is present when Queen Cersei holds court, and moves to protect his queen when Euron Greyjoy steps too close to the throne.

He is also present when Cersei holds court to the nobility of The Reach.

Ser Gregor was also present when Queen Cersei hosts a grand reception with Lord Euron and his prisoners Yara Greyjoy, Ellaria Sand, and Tyene Sand. He was later present in the dungeons with Qyburn when Cersei confronts her prisoners Ellaria and Tyene over the murder of her daughter Myrcella Baratheon. While Cersei had toyed with ordering Ser Gregor to smash their heads like he did with Oberyn Martell, she instead settled for poisoning Tyene with the Long farewell and forcing Ellaria to watch her daughter's final death throes. When Daenerys Targaryen and her retainers were set to arrive in King's Landing to negotiate an armistice with Cersei and her royal army, Cersei has Clegane stand in as her personal bodyguard. Even before they set out to the Dragonpit, where the meeting is stated to be held, she makes preparations with Qyburn, Jaime and Clegane. She orders Ser Gregor to first kill Daenerys, then Tyrion, then Jon, and the rest of them in any order if the meeting goes wrong. Together with Clegane, Cersei then sets out to meet their guests. When their procession arrives in the Dragonpit, Sandor Clegane—who is with the group of Daenerys—is shocked to see the state of his hated brother. Once Gregor has taken his place behind Cersei, Sandor approaches him. Sandor hatefully states that Gregor was now uglier than Sandor and that this was not how it would end for Gregor. Sandor continues, claiming Gregor knew that Sandor will be coming for him, before returning to his group. Accordingly, Gregor steps back behind Cersei, only to emerge once more when Daenerys arrives on the dragon Drogon.

When Euron Greyjoy takes too many liberties during the parley, threatening the fragile peace, Cersei orders him to sit down or leave. Clegane threateningly makes a step forward to further stress her point. During the parley, Daenerys's group releases a wight to prove the threat the undead pose. Clegane was ready to shield Cersei from the wight, but Sandor yanks it back with a chain.

When Jon Snow later reveals to Cersei that he already swore allegiance to Daenerys, Cersei calls off the parley and returns to the Red Keep with her retainers, Clegane included. To convince her to accept the armistice, Tyrion follows her and is escorted to her chambers by Clegane, who visibly makes Tyrion uneasy. Clegane escorts Tyrion into the room and remains in the back while Cersei and Tyrion argue and discuss. He is ready to execute Tyrion when the dwarf demands he do so, but Cersei never gives the order. Instead, Tyrion actually manages to convince Cersei to come to the Dragonpit again and, accompanied by Clegane and the others, Cersei turns up once more to announce that she will send her armies north to assist in fighting the dead. This, however, is a lie and Cersei has no intention of doing so. The group returned to the Red Keep. When Jaime made it clear to Cersei that he would join the fight against the Army of the Dead with or without her, Clegane suddenly prevented him from leaving the room. Cersei calls Jaime a traitor for disobeying her commands and stating that no one walks away from her. When Cersei nodded, Clegane draws his sword, waiting for Cersei to give the order to execute Jaime. However, Jaime called Cersei out on her bluff and walks right past Clegane, who does not intervene, and out of the room.

Season 8
Ser Gregor is present when Euron Greyjoy and Captain Harry Strickland announced the arrival of the Golden Company to Cersei. Afterwards, Euron makes another move on Cersei, but Clegane stopped him from proceeding with a menaceing stare. Nevertheless, when the Queen finally allows Euron to have his way with her, Clegane did not intervene. While the Unsullied besieged King's Landing, Gregor carried out Cersei's order of executing Missandei.

During the Battle of King's Landing, Gregor stays by Cersei's side to guard her. After Qyburn convinces her to flee from the Red Keep, he protected them both from the debris falling as a result of the Red Keep crumbling due to Drogon's attack. They are however confronted by Sandor who slays all the surviving Kingsguard except Gregor who remained at Cersei's side.

Gregor wishes to fight Sandor but Cersei and Qyburn order him to guard her. In anger, he crushed Qyburn's skull while Cersei fled past both of the brothers. In the ensuing duel, Sandor proved himself better at sword fighting than Gregor and stabs him, but he doesn't die due to his reanimation. Gregor proceeds to brutally thrash and choke Sandor who stabs him many times in vain. While trying to crush his eyes, Gregor was stabbed in his left eye and toppled high off Red Keep's tower by Sandor who fell along with him onto the burning ground.

​Personality and traits​
"I wanted him to chase us, which he would have done because he is a mad dog without a single strategic thought in his head."

- Robb Stark aptly describes the Mountain. Gregor is well-known for his brutal and savage nature, remorselessly killing unarmed opponents half his size or leading the torture of helpless villagers. Often referred to as "Tywin Lannister's mad dog", Gregor has an insatiable bloodlust that he releases through acts of extreme violence. He is quick to anger and never shows any fear of acting on it, since no one dares stop him. One of the only people he has ever shown any loyalty or respect toward is Tywin; when not actively obeying Tywin's orders he mostly acts of his own accord, showing even little respect toward King Robert Baratheon after he was told to stop his fit of rage at the Tourney of The Hand. Gregor is also loyal to Qyburn and Cersei, following the experiments performed on him to prevent his death. His extremely violent and ruthless personality had even manifested as a child, quickly becoming known for his superhuman strength and incredibly massive size. Gregor even burned his own brother's face when they were children simply for playing with one of Gregor's toys. Tywin suggests that Gregor is also an alcoholic, when instructing Arya Stark to keep Gregor from getting drunk.

Gregor's short fuse and utter lack of a conscience often showed his lack of honor, such as when he tried to murder Loras Tyrell after already losing a joust against him. In addition, Gregor does not appear to be very bright, relying solely on his physical instincts to get the job done without thinking of the long-term consequences, shown when he furiously bellows out for all to hear that he in fact did commit arguably his most infamous war crime while murdering Oberyn Martell, unaware that until then it was merely a rumor and will have severe consequences if the truth were to come out. Robb Stark describes Gregor as a "mad dog without a strategic thought in his head", while Jaime Lannister quips that Gregor had difficulties understanding complete sentences. It is ironic that it is Sandor Clegane who is nicknamed 'The Hound' when Sandor is at least capable of logical speculation and common sense, and it is Gregor who is at the absolute mercy of his animalistic rages and impulses.

As a warrior, Gregor is widely feared for his terrifying and gigantic size and superhuman strength. He is a giant of a man, standing well over seven feet in height (eight feet in the novels) and weighing over 500 pounds. In combat, his immense strength and beastly size gives him a huge advantage over almost any opponent, which allows him to defeat men who have far more skill. His weapon of choice is an enormous great sword that most men would never be able to swing with even two hands, but which Gregor is strong enough to wield one-handed. He is strong enough to decapitate a horse with a single swing of his sword, as seen during his joust with Loras Tyrell. Gregor also wears armor larger and thicker than normal knights would be able to wear, providing him almost impenetrable defense against his opponents. However, his brother Sandor Clegane (who is also incredibly large and strong, though not to the same extent as Gregor) was shown to be able to duel him evenly. In addition, Gregor's lack of technical skill allowed Oberyn Martell to overwhelm him in their duel, as Oberyn's unique style of combat relied heavily on maneuverability and he used a spear to stay out of Gregor's reach.

Following being poisoned by Oberyn's Manticore venom, Gregor is experimented on by Qyburn to keep him from death. The process changes Gregor as was expected. It is unclear whether he is truly alive or not. The Mountain becomes a "new" man and now part of Cersei's guard. Other than his soulless eyes and black, partially decayed flesh visible through his helmet, he can not be seen under his full body armor, however, his face is seen in the Red Keep dungeons after he is instructed to remove his helmet by Cersei. Whatever he is now, he is completely in service to Cersei (and Qyburn), and serves them in silence. Qyburn claims that he has vowed not to speak until King Tommen's enemies and all evil are gone from the realm. It is at least as likely that he is no longer capable of speech, not that he spoke much before anyway. Furthermore, it appears that far from weakening him, the process Qyburn subjected Ser Gregor to has made him even stronger than he once was; when a faith militant attacks him and manages to pierce his armor, he doesn't even flinch or acknowledge it, instead he just literally tears the man's head off in retaliation. Gregor was also shown to be impervious to impalement throughout his body even when unarmoured as he was repeatedly stabbed in various areas of his torso by his brother Sandor to no effect, the only time he was visibly affected was when Sandor stabbed him through the eye, however, this still didn't kill him.

As revealed during the recent events at King's Landing, Ser Gregor still retains his own will and sense of self, as he defied the Queen's orders and even killed Qyburn just to fight his brother. Gregor's individuality and "intelligence" post transformation has been hinted at before, as when Jaime made a snide comment about him in a conversation with Qyburn, Gregor instantly turned his head to glare at Jaime, showing he wasn't completely devoid of sentience or independent actions.

Quotes
"Sword!"
 * Spoken by Gregor

- Gregor Clegane to his squire.

"Taller by a foot than any man I've ever met. Saw him cut the blacksmith in two, saw him take the head off a horse with a single swing of his sword."
 * Spoken about Gregor

- Joss describes Gregor.

"See that he doesn't get drunk in the evenings. He's poor company when he's sober, but he's better at his work."

- Tywin to Arya Stark about Gregor.

"Years after, servants started disappearing in our keep. And even a sister, I don't remember. But nobody could prove anything against Gregor, or dared if they caught him at it."

- Sandor Clegane talks about Gregor.

"I wanted to draw the Mountain into the West, into our country, where we could surround him and kill him. I wanted him to chase us, as he would have done because he is a mad dog without a strategic thought in his head. I could have had that head on a spike by now."

- Robb Stark emphasizes Gregor's lack of intelligence which could have been used against him to Edmure Tully.

"May I have the honor of presenting the newest member of the Kingsguard? If it please, Your Grace, he's taken a holy vow of silence. He's sworn that he will not speak until all His Grace's enemies are dead, and evil has been driven from the realm."

- Qyburn to Cersei about the new Gregor.

"This is Ser Gregor Clegane. He's quiet too. Your gods have forsaken you. This is your god now."

- Cersei introducing Gregor to Unella.

"Remember me? Yeah, you do. You're even fucking uglier than I am now. What did they do to you? Doesn't matter. It's not how it ends for you, brother. You know who's coming for you. You've always known."

- Sandor Clegane to Gregor.

Behind the scenes

 * Gregor Clegane is the only character in the entire series who has been portrayed by more than two actors in different seasons. He was initially played by Conan Stevens. The second actor, Ian Whyte, was originally to continue portraying the character after the second season, but was instead cast as Dongo and later Wun Weg Wun Dar Wun. Whyte's replacement, Hafþór Júlíus Björnsson, is actually nineteen years younger than Rory McCann, who portrays Gregor's younger brother Sandor Clegane. From the three, only Stevens and Björnsson have shared screen time with McCann as their respective characters.
 * Michael Homick was a stunt double for Hafþór Júlíus Björnsson in the role of Gregor Clegane.

In the books
In the A Song of Ice and Fire novels, Ser Gregor Clegane is a savage brute of a man, freakishly tall at nearly 8 feet in height, and well over 30 stone in weight (420 lbs./190 kg), most of it muscle. Gregor is so strong that he can easily wield with one hand greatswords which are meant to be wielded with two hands, allowing him to carry a shield as well. He is so strong that he has been known to cleave men in two with a single blow of his sword.

Known as "the Mountain That Rides", Gregor is one of Tywin Lannister's chief enforcers. Gregor's knighthood is regarded as a hypocritical mockery of justice by many, as he is a thoroughly dishonorable and undisciplined butcher. While Gregor is so strong that he can easily fight the strongest knights in Westeros, his greatest enthusiasm in wartime is for burning out the homes of peasants who cannot possibly fight back, and torturing their women and children to death. Indeed, Gregor's immense size isn't really his main attribute to Tywin, so much as his utter enthusiasm for committing atrocities. With a "might makes right" mentality, Gregor feels that his immense bulk and strength gives him impunity to behave as he does, as few would dare to challenge him. While Gregor is incredibly dangerous in combat, he relies more on sheer strength than on speed or skill. Gregor has gone through multiple wives, who died from the extremely rough treatment they received from Gregor, though there are rumors that he killed them on purpose. His father and younger sister also died suspiciously. Sandor Clegane left when Gregor succeeded their father and never returned.

Gregor has a nearly uncontrollable temper, and is capable of very brutal violence for the slightest provocation. According to Sandor, he once killed one of his men for snoring. When he was in Harrenhal, a servant girl named Pia spoke when he wanted silence, so he smashed her face in with his mailed fist, breaking her nose and many of her teeth.

Gregor's men-at-arms are known as "The Mountain's men". His cruelty and brutality are clearly mirrored in them. The best thing that can be said about them is that they are less vile and violent than the Brave Companions, Vargo Hoat's sellsword company. Those who are mentioned specifically in the books are:
 * Joss Stilwood, his squire.
 * {Rafford} aka Raff the Sweetling, who killed Lommy. Killed by Arya Stark.
 * Dunsen, who took Gendry's bull helm.
 * {The Tickler}, a torturer. Killed by Arya Stark.
 * {Polliver}, who took Arya's sword. Killed by the Hound, in the same fight that Arya kills the Tickler.
 * {Chiswyck}, who assisted the Tickler with the torturing. Killed by Jaqen H'ghar.
 * Shitmouth, the most foul-mouthed of Gregor's soldiers, but less cruel than the rest. Gives extra food to captives if they ask him nicely.
 * Eggon
 * Tobbot
 * {Unnamed squire} of House Sarsfield. Killed by Arya Stark
 * Two others, one castrated and the other executed for committing rape and murder in Maidenpool on the orders of Randyll Tarly.

When Sandor escorts Sansa back to the Red Keep after the tournament feast, at Joffrey's command, he tells her the story of how his face was burned (not Littlefinger as happens in the TV series): a wood carver gave toys to both of the Clegane children in order to gain their father's patronage. Sandor wanted the articulated jointed knight that Gregor got, so he took it. Gregor was ten and already big enough to be training so he didn't even care about the toy, but when he found six year old Sandor playing with it - without warning he pushed Sandor's head into a brazier and held him there. It took three men to get Sandor away from him, and their father told people that Sandor's bed linens had caught fire. It was later when Gregor was anointed a knight that Sandor Clegane lost all respect for the institution of knighthood, and has steadfastly refused to be knighted himself.

Sandor also tells Sansa that the death of Hugh of the Vale was not a tournament accident. Ser Hugh had obviously put on the armor himself and had not set the neck protector correctly. He says Gregor saw that, and thus could have sent the blow elsewhere, and that the lance didn't just accidentally deflect upward, as Gregor puts his lance exactly where he intends it to go every time. He meant to kill Ser Hugh, though it isn't clear if this was an assassination to silence Hugh, or just Gregor enjoying the carnage.

In the second novel, Tyrion offers Doran Martell, among other things, Ser Gregor. Tywin disapproves, claiming that Gregor has his uses, and every lord has need of a beast from time to time. Tyrion answers that "the woods are full of beasts", and Tywin says he'll think it over. Later, Tywin decides against the idea, stating that "Ser Gregor has served us well. No other knight in the realm inspires such terror in our enemies"; in order to appease the Martells, he comes up with the idea to put the entire blame on Amory Lorch (who is, quite conveniently, dead). As things turn to be, Tywin's new version of the death of Elia and her children does not stop Oberyn from fighting Gregor.

Reanimated as Ser Robert Strong
While treating Gregor Clegane, Qyburn theorizes that Oberyn had adulterated the manticore venom on his spear with sorcery; thickening it in order to slow its progress through the veins towards the heart, dragging out Gregor's agony. It is also not at Cersei's orders but Tywin's that Gregor is treated, though this is only to get him enough back to health so Ilyn Payne could execute him. After Gregor's public confession of his part in the murders of Elia Martell and her children, Tywin (who had always dismissed such talk as malicious rumors) intended to publicly execute Gregor in order to appease House Martell, rather than risk their outrage at Elia and Oberyn's deaths causing Doran Martell to support Stannis Baratheon (though Tywin was killed by Tyrion before this could happen).

After Loras is sent to resolve the siege of Dragonstone, Qyburn tells Cersei that in case Loras dies, she will need to find another worthy for the Kingsguard. He claims "I had another sort of champion in mind. What he lacks in gallantry he will give you tenfold in devotion. He will protect your son, kill your enemies, and keep your secrets, and no living man will be able to withstand him". Cersei is skeptical; she orders a gigantic suit of armor at Qyburn's request -despite the blacksmith's insistence no living man can move or fight under such weight- but warns him that if he plays her for a fool, he will pay dearly.

As a gesture of good will, Cersei assigns Ser Balon Swann to deliver a huge skull to the Martells, which the Lannisters claim is Gregor's, and most of them accept that Gregor has finally been punished for his crimes (though it is a little consolation to Ellaria, who deeply mourns Oberyn). Only Obara is skeptical, suspecting a deception. Nymeria tells her half-sister to lighten up, as Gregor was the only 8-foot tall man in all of Westeros, and Cersei would be exposed as a liar before the entire continent if it turned out he was somehow still alive. What Nymeria says makes perfect sense, except that Cersei is far from being rational and clever. Obara has no idea how much she is close to the truth.

Following Cersei's downfall, Qyburn visits her in prison and informs her new champion stands ready. Cersei laughs bitterly, since she can be defended only by a sworn brother of the Kingsguard, but Loras somehow clings to life despite his mortal wounds, thus she cannot make a use of her invincible champion. However, when she hears from Kevan about Ser Arys Oakheart's death, she sees a chance of survival: there is an empty place on the Kingsguard that must be filled. She begs her uncle to have Tommen appoint a man whom Qyburn knows his name.

Following Cersei's walk of penance, Qyburn introduces her to Ser Robert Strong, a man clad from head to toe in white armor (no part of him is visible) and matching Gregor's physique. According to Qyburn, Strong has taken a holy vow of silence until all of King Tommen's enemies are defeated. Many people, including Kevan Lannister and Grand Maester Pycelle, theorize that Strong is actually Gregor, or maybe even a Frankenstein's monster assembled from Gregor's body as well as other bodies. In an earlier book, Bran Stark has a vision of Strong, and when his visor lifts, there is only darkness and black blood, leaving it ambiguous as to whether or not Strong even has a head.

In the television series, Cersei's new Kingsguard is not given a name, and what is seen of his face through his helmet matches that of Gregor, somewhat confirming that Gregor and Strong are the same man. In the sixth season of the series, he is still referred to as Gregor Clegane, the Robert Strong name having been dropped entirely.

While in the novels the murder of Rhaenys Targaryen is assigned to Ser Amory Lorch, another knight in the service of Tywin Lannister, the TV-series omitted this and Gregor is blamed for the death of Elia, Aegon and Rhaenys.