Elia Martell

"My sister, Elia, she married Prince Rhaegar Targaryen and became the princess she already was. In Dorne, she walked among vipers and none would bite her. In King's Landing, she found herself surrounded by lions."

- Oberyn Martell

Elia Martell is an unseen character in Game of Thrones. She is deceased when the events of the series begin and is not expected to appear.

Background
Princess Elia was the wife of Prince Rhaegar Targaryen. They had two children; a daughter Rhaenys Targaryen and a son Aegon. She was born into House Martell in Dorne. She was the younger sister of Prince Doran Martell, the current ruler of Dorne, and an older sister of Prince Oberyn. Her marriage to Prince Rhaegar was arranged by King Aerys II Targaryen and considered an insult by Tywin Lannister, Aerys's Hand of the King, who had proposed his daughter Cersei as a bride for the Prince but was rejected. The marriage was one of the reasons Lord Tywin resigned his post as Hand. Like her younger brother, Elia was very popular among the Dornish people

As a teenager, Elia accompanied her brother Oberyn on a visit to Casterly Rock. While there, Elia and Oberyn were eager to see the monster that had just been born. Cersei finally showed them the baby, but the Martell siblings were somewhat disappointed to see that Tyrion was just a baby, and somewhat disturbed by Cersei's already strong hatred of him.

Elia loved her husband Prince Rhaegar dearly. She bore him two children, Rhaenys and Aegon, to whom she was equally devoted; according to Oberyn, Elia took care of them from birth, rather than delegating the task to a wet nurse. Both pregnancies were very difficult, and each nearly killed Elia. When Robert's Rebellion erupted, Elia was kept in King's Landing by King Aerys to ensure the loyalty of House Martell during the conflict- a measure the Martells considered unnecessary, as they would always fight for whichever side Elia was on and had no intention of breaking their oaths of loyalty to the Targaryens. Ultimately Rhaegar was killed in personal combat with Robert Baratheon at the Battle of the Trident, leaving Elia widowed. A few weeks later during the Sack of King's Landing, Tywin Lannister's army betrayed the Targaryens and overran the city. Ser Gregor Clegane - known as "The Mountain That Rides" burst into the royal chambers and before Elia's eyes, killed her daughter Rhaenys, then bashed her infant son's head in against a wall. Covered in the blood and gore of her children, Gregor proceeded to brutally rape Elia, and finally he killed her. It is rumored that he cut her in half with his greatsword, though Gregor himself later confesses to "smashing her head in".

Elia's death deeply alienated her family from the crown after Robert ascended the throne, and their hatred of the Lannisters now knew no bounds. Subsequently they were never seen and rarely if ever mentioned at the royal court in King's Landing.

Season 4
Elia is mentioned many times by her brother Oberyn in his conversations with various members of House Lannister. It becomes clear that Oberyn loved his older sister very much. When speaking to Tyrion, Oberyn expresses apparent anger that "beautiful, noble Rhaegar Targaryen left her for another woman" despite Elia's love and loyalty for Rhaegar. Oberyn tells Cersei that his fifth daughter is named for her, and that he finds it difficult to interact with her as a result.

Upon learning that the Mountain will act as Cersei's champion at Tyrion's trial by combat, Oberyn volunteers to be Tyrion's Champion, hoping he will finally have vengeance for his sister.

During the trial by combat, Oberyn's rage is fueled by his desire for vengeance of his sister's murder. He repeatedly shouts "You raped her! You murdered her! You killed her children!" towards Gregor, in order to make him confess in front of the crowd. This personal vengeance does not work in Oberyn's favor, as he becomes too confident during the fight and makes a mistake, inevitably leading to his brutal death. As he kills Oberyn, Gregor callously admits, for all the crowd to hear, that he raped Elia, killed her children and then smashed her head in, effectively confirming the long-standing rumor of arguably his most infamous war crime.

In the books
In A Song of Ice and Fire, Elia is also the wife of Rhaegar, and died with her children in the Sack of King's Landing. She was the sister of Princes Doran, the ruling Prince of Dorne, and Oberyn Martell. Elia was born nine years after Doran, and a year before Oberyn.

During Robert's Rebellion, Gregor Clegane raped and killed Elia after bashing in her son's head, while his hands were still tainted with the infant's blood. Elia's daughter was killed by Amory Lorch.

Tywin Lannister later admitted to Tyrion that there was no need to kill Elia because "by herself she was nothing" (in contrast to her children - as Rhaegar's blood heirs even Robert knew they had to die for the war to end). The Mountain killed Elia simply because Tywin did not tell him to spare her. Tywin doubted if he had mentioned Elia at all, for he had many pressing concerns to worry about at that time, nor did he yet realize what kind of monster the Mountain was. On the other hand, he never punished Gregor for the rape and murder, because that would be an admission of indirect guilt on his part. This of course backfired: his inaction only served to convince the Martells that he was actively responsible and must have directly ordered Gregor to kill Elia, harming relations with the Martells far more than if he had simply admitted the truth. Tywin was also uncharacteristically defensive when Tyrion voiced his suspicion that he ordered Gregor to not only kill Elia, but rape her first, showing that even he was disgusted by what Gregor did (but still did not punish him for it).

The Martells (particularly Oberyn) were so outraged by Elia's brutal and needless murder that they initially intended to continue fighting in Viserys Targaryen's name. After the rebellion's end, Jon Arryn's first act as Hand of the King of the King was to travel to Dorne and negotiate with Prince Doran; Arryn convinced the Dornish to cease hostilities, but the fact Elia's killers were never punished caused the region to adopt a largely isolationist policy with the rest of the Seven Kingdoms.

As part of the Lannister alliance with the Martells that he negotiates, to prevent them from joining Renly's host, Tyrion pledges to bring those responsible for the death of Elia and her children to justice, including the Mountain. Tywin later reneges on this, intending to place all the blame on the now-deceased Amory Lorch. Oberyn does not seem to believe that new version, and Tyrion assures him that Lorch killed Rhaenys, while the Mountain killed baby Aegon and then proceeded to rape and kill Elia. After Gregor roars his guilt for all to hear during Tyrion's trial by combat, Tywin is forced to have Gregor healed if only so Ilyn Payne can execute him to appease the Martells, for fear inaction might lead to Dorne supporting Stannis Baratheon's cause.