Black Walder and Lothar Frey are sent to Riverrun by Lord Walder Frey to negotiate with Robb Stark the terms for the Freys' re-entry into the Northern army. Black Walder bluntly demands that Harrenhal and all its attended lands to be inherited by House Frey for Robb Stark's "betrayal" in breaking his oath. Black Walder further demands that Edmure Tully be engaged to one of Lord Walder Freys's daughters, with the pair to be married within the fortnight due to the fact that Lord Walder had become wary of long engagements after his recent experience with Robb Stark. Before taking their leave, the pair demanded a response to their terms before they departed for The Twins the following morning. 
During the aftermath of the Red Wedding, Catelyn Stark murders Walder Frey's wife by cutting her throat in grief of Robb's death after Roose Bolton stabs him through the heart with a dagger. Catelyn lets out a wail of tears and remains silent for a moment, before Black Walder steps behind her and cuts her throat and walks away as the blood spews out of her. 
Black Walder and Lothar inform their father of the capture of Riverrun by Ser Brynden Tully. When Lord Walder berates them for allowing the Blackfish to escape in the first place, Black Walder begins to protest but his father cuts him off and demands they take back Riverrun. They argue that, since House Mallister and House Blackwood are supporting Brynden, and Riverrun is built to withstand sieges, retaking the castle would be impossible. Walder tells his bastard to take Riverrun by showing Brynden the knife he used to cut Catelyn's throat, and by using the captive Edmure as a bartering piece.
Black Walder and Lothar siege Riverrun as commanded, but do a poor job of it. They do not fortify their boundaries, allow the Lannister army to enter unnoticed, and do not even dig trenches. To try and force Brynden to surrender, Walder stands on a scaffold with Edmure and threatens to hang him. When this fails, he threatens to cut his throat as he did to Catelyn. Brynden calls his bluff, knowing that Edmure is too valuable to kill, and the siege continues. Ser Jaime Lannister arrives to take over from the Freys, but is immediately challenged by Walder. Jaime contemptfully calls Walder a fool for making threats he wasn't prepared to carry out and orders him to be silent. When Rivers keeps talking, Jaime hits him, and Walder begrudgingly follows his and Bronn's orders, although he is clearly unhappy.
Black Walder is later seen at The Twins, where the Lannisters and the Freys celebrate their successful siege of Riverrun. He is later killed by Arya Stark, who minces his flesh and bakes him into a pie together with his brother, Lothar. She then serves the pie to their father, who eats at least one helping before Arya brings another and reveals what she had done, commenting that they were not easy to carve, especially Black Walder. Arya then reveals her identity to Lord Walder and slits his throat as Black Walder once did to her mother.
Lothar and Black Walder's remaining male family members are poisoned by Arya, who hosts a banquet using the face of their father.
|Season Three appearances|
|Valar Dohaeris||Dark Wings, Dark Words||Walk of Punishment||And Now His Watch Is Ended||Kissed by Fire|
|The Climb||The Bear and the Maiden Fair||Second Sons||The Rains of Castamere||Mhysa|
|Season Six appearances|
|The Red Woman||Home||Oathbreaker||Book of the Stranger||The Door|
|Blood of My Blood||The Broken Man||No One||Battle of the Bastards||The Winds of Winter|
- Black Walder: "Edmure is a prisoner of House Frey."
- Jaime Lannister: "Only a fool makes threats he's not prepared to carry out. Now, let's say I threatened to hit you unless you shut your mouth but you kept talking: what do you think I'd do?"
- Black Walder: "I don't give a rat's-! (Jaime hits him in the face)"
- Jaime Lannister: "I'm here by the King's command to take back this castle. Have him bathed and fed...unless you'd like to take his place?!"
- — Jaime Lannister berates Black Walder for his incompetence during the siege of Riverrun.[src]
In the books
"Black Walder Rivers" in the TV series is a composite of two different Frey characters from the A Song of Ice and Fire novels: "Black" Walder Frey, Lord Walder's great-grandson and grandson of Stevron Frey, and Ser Walder Rivers, Lord Walder's eldest and most prominent bastard son, known as "Bastard Walder" for obvious reasons. The character who appeared in the TV series was named as "Black Walder" in Season 3, though the HBO Viewer's Guide referred to him as a bastard son, not a trueborn great-grandson. The updated Season 4 Viewer's Guide website clarified this by identifying him as "Black Walder Rivers".
Black Walder Frey
Black Walder's father, Ryman, is the eldest son of Ser Stevron Frey, who is himself the eldest son, and heir, of Lord Walder Frey. Thus Ryman's three sons - Edwyn, Black Walder, and Petyr - are the presumptive future heirs of House Frey (which includes over a hundred direct descendants of Lord Walder). At the beginning of the first novel, Black Walder is fourth in line to succeed Lord Walder, behind his grandfather Stevron, his father Ryman, and his older brother Edwyn. While Edwyn is ahead of Black Walder in the line of succession, he is not a fierce warrior like Black Walder is, and the two of them are constantly jockeying for power and favor within the family. As a result, Black Walder is one of the more prominent members of House Frey.
Black Walder is a stern and wiry man with a black beard, who inspires terror in those around him. Black Walder is known to be resolute and easy to anger, being feared by many among his own family. He is rumored to have maintained numerous affairs with several women, including cousins and the wives of his close relations, even his full brothers' wives. In particular, it is strongly rumored that Black Walder had an affair with Lord Walder's seventh wife, Annara Farring, and that he is the true father of all six of her children (including Shirei Frey, allegedly Lord Walder's youngest daughter).
Black Walder took part in the Red Wedding. Prior to the massacre, Robb remarked to Catelyn that he was surprised that despite his normal disposition, Black Walder was acting like a lamb during the festivities - not realizing that for Black Walder to behave so out of character was a hint that he was trying too hard to allay the Starks' suspicions that the Freys were planning something. Prior to the wedding, Black Walder had gone so far as to remark that his sisters would not be loathe to marry a widower - implying that they should simply kill Robb's new wife so he would be free to marry a Frey girl again. Robb said he would have killed Black Walder for such an insult, but his wife begged him to show mercy.
During the chaos of the resulting massacre in the feast hall, Catelyn catches a quick glimpse of Black Walder hamstringing a member of House Vance, who are vassals of the Tullys.
Black Walder is the one who forces Lord Jason Mallister to yield Seagard, by threatening to kill his son Patrek Mallister, who was taken captive at the Red Wedding. He does not take part in the siege of Riverrun (in the show he does, replacing Ryman Frey).
After Black Walder's father Ryman is killed by the Brotherhood without Banners, Ryman's eldest son Edwyn becomes the heir of Lord Frey. Edwyn suspects that Black Walder has played a role in their father's death, and fears that he is the next to die.
Black walder is still alive by the point the books reached. He is not one of the three Freys (Jared, Rhaegar and Symond) who are allegedly killed by Wyman Manderly, as a payback for his son's death at the Red Wedding, then baked into pies and served at Ramsay's wedding.
Another difference with the TV series is that neither Black Walder, who was in the main hall, nor Walder Rivers, who was off fighting in the camps outside, personally killed Catelyn Stark. Instead, Catelyn was so devastated by seeing Robb killed in front of her that she went mad, crying and laughing hysterically, and clawing away strips of flesh from her face. The surrounding Freys were so horrified that one of them openly asks for someone to kill her quickly to put her out of her misery, despite the fact that Tywin Lannister wanted Catelyn taken as a hostage. The man who slits her throat in the books was Raymund Frey, Lord Walder's eleventh son, the sixth son born out of his wedding to Amarei Crakehall. Raymund Frey is a fairly minor character, however, and other than slitting Catelyn's throat he has no other appearances or role within the narrative. Therefore, the TV series simply gave the role of slitting Catelyn's throat to Black Walder, given that he is also in the main hall in the books - and then Black Walder was combined with Walder Rivers to make "Black Walder Rivers".
Ser Walder Rivers is the eldest and most prominent of Lord Walder Frey's bastard offspring. His mother is an unidentified woman who died after falling off a horse. He is a gruff, dour man with grey hair and his father's suspicious face, resentful of his baseborn origins, and hates everyone who is trueborn. Though not a trueborn Frey, he is often put in positions of responsibility for the house due to his strong reputation as a warrior.
His personal coat of arms follows the tradition of heraldry for bastards by reversing the colors of his noble parent's House: a silver-grey castle on blue beneath a red bend sinister. The TV series changed the House Frey heraldry: in the books, it is the two towers and bridge of the Twins colored blue, on a silver-grey background. The TV series made the towers white, and over the same grey field, but now above a blue escutcheon which is drawn to resemble the waves of the Green Fork of the Trident River. The color change may be because after the blue river was added as an escutcheon at the bottom, it would have been visually confusing to have the castle be the same color as the water. Unfortunately this makes the Frey sigil in the TV series resemble the reversed color-scheme used by bastards in the books. If the TV series were to follow the same scheme of reversing the established color-scheme of a sigil for bastards, Walder Rivers' sigil would be a blue castle on a silver-grey background.
In the third book, it is Walder Rivers who accompanies his half-brother Lame Lothar to Riverrun, not Black Walder. While they converse with the Starks, Walder Rivers barely contributes to the conversation, leaving it to Lothar to deliver Lord Frey's offer; when he finally speaks, his tone is very blunt, in contrast to Lothar's tactful words.
During the Red Wedding, Walder Rivers commands the assault on the Stark soldiers' camps outside of the Twins.
In the fourth book Walder Rivers takes part, though rather minor, at the siege of Riverrun, alongside his nephew Ryman and his great-nephew Edwyn Frey. Jaime takes one look at him and concludes "That one is more dangerous than any of his trueborn brothers".
Walder Rivers is still alive by the point the books reached.
- Walder Frey (son of Ryman) on A Wiki of Ice and Fire (MAJOR spoilers from the books)
- Walder Rivers on A Wiki of Ice and Fire (spoilers from the books)
- Raymund Frey on A Wiki of Ice and Fire
|Seat:||The Twins · Riverrun||Lands:||Riverlands|
|Title(s):||Lord of the Crossing · Lord of Riverrun · Lord Paramount of the Trident|
|Current members:||Arwaya Frey · Derwa Frey · Freya Frey · Janeya Frey · Marianne Frey · Merry Frey · Neyela Frey · Olyvar Frey · Roslin Frey · Sarra Frey · Serra Frey · Shirei Frey · Walda Frey · Waldra Frey · Waldron Frey · Ryger Rivers|
|Deceased members:||Joyeuse Erenford · Lothar Frey · Walda Frey · Walder Frey· Walder Rivers|
|Household:||Malcolm · Talbot|