Ser Brynden Tully is a knight and a member of House Tully. He is the younger brother of Lord Hoster Tully, and the uncle of Catelyn, Lysa, and Edmure Tully.
Brynden Tully is the younger brother of Hoster Tully. Hoster is the Lord of Riverrun and the head of House Tully. He is the uncle of Catelyn Stark, Edmure Tully, and Lysa Arryn. Brynden is a respected knight and formidable battle commander, who first distinguished himself in the War of the Ninepenny Kings (nearly forty years before the War of the Five Kings).
Brynden often argued with his older brother Hoster, particularly over the fact that Brynden never married. When Brynden returned home from the War of the Ninepenny Kings, Hoster had already arranged for him to marry Bethany Redwyne, of the wealthy and powerful House Redwyne. Brynden refused this generous match, however, refusing to be told when and whom to marry. Hoster was angry that Brynden would not do his duty to their family and enter into a marriage-alliance to improve their fortunes, and said that he was the black goat of the Tully herd. Brynden joked that given that the Tully sigil is a trout, it would be more fitting to say that he was the "black fish" of the Tully school. The nickname stuck, and Ser Brynden became popularly known as "The Blackfish" ever since. Brynden even took to using a black fish in his own personal heraldry: like the standard Tully heraldry it uses a red and blue background, but swaps out the normal silver trout for a black one. Hoster would attempt to contract other arranged marriage-alliances for Brynden over the years, many of them very promising matches, but Brynden turned down them all, which led to constant bickering between the two brothers throughout their lives.
Despite his disagreements with his brother over his refusal to marry, Brynden is very devoted to his family.
During the funeral of Hoster Tully, an annoyed Brynden takes the place of his nephew, Lord Edmure, after the latter fails several times to hit the funeral boat with flaming arrows. Later on he also chides Edmure for calling Robb "nephew" instead of treating him as his King as Edmure defends his course of action that led to the Battle of Stone Mill. He also consoles Catelyn when she muses about her father's funeral and whether she will ever see Bran and Rickon, whose whereabouts are unknown following the Sack of Winterfell.
The Blackfish brings Rickard Karstark and his men before King Robb after they brutally murdered Willem and Martyn Lannister as revenge against House Lannister. Brynden is highly offended when Karstark calls King Robb "boy" and punches him in the face in retaliation. Brynden counsels King Robb not to execute Lord Karstark but instead to keep him as a hostage, thus keeping the Karstark forces loyal to the Starks. King Robb disagrees, however, and executes Lord Karstark under charges of treason while Brynden watches on along with Edmure, Talisa and Catelyn.
The Blackfish is again present when "Black Walder" and Lothar Frey come to Riverrun to discuss an alliance between House Stark and House Frey. The Freys demand that Edmure must marry one of Lord Walder Frey's daughters if the alliance is to go ahead. Edmure is reluctant to agree to these terms but Brynden tells him that he must if they have any hope of winning the war.
En route to the Twins for Edmure's wedding, Brynden agrees with Catelyn that Walder Frey is the prickliest man he has ever met. He states that he has seen "wet shits I like more than Walder Frey".
During the wedding feast, he goes outside to relieve himself on a tree. He escaped the massacre of Robb Stark, Talisa Stark, Catelyn Stark, and all their soldiers during the Red Wedding. His whereabouts are unknown.
Lord Petyr Baelish informs Sansa Stark that Brynden has reunited the remnants of the Tully army and successfully taken back Riverrun from House Frey, and he advises her to seek her uncle out for help retaking the North. Heeding this advice, Sansa sends Brienne of Tarth to meet with Brynden.
Lord Walder Frey berates his sons for losing Riverrun, and requests help from the Lannisters in taking it back, thus beginning the Siege of Riverrun. While parleying with Jaime Lannister, the Blackfish informs him that Riverrun can hold out for two years, and that he must be ready to lose thousands of men if he wants to storm Riverrun. Realizing that the Blackfish has no intention of surrendering, Jaime is furious that he had to meet him at all.
Later, Brienne of Tarth arrives with Sansa Stark's letter, asking the Blackfish to send his forces North to join Sansa and Jon's army. The Blackfish refuses to give up Riverrun, even for his great niece. Edmure is sent to retake the castle from the Tully garrison, under threat of the murder of his son. The Blackfish knows that Edmure is not coming of his own free will, and orders the men not to let him in. Though the Blackfish commands the forces at Riverrun, formal authority is vested in Edmure as the rightful head of House Tully and the Lord of Riverrun, and his men are obliged to obey Edmure, not the Blackfish. Edmure orders his men to surrender and that his uncle be put in chains, but the Blackfish refuses to surrender and resolves to kill as many men as he can. He helps Brienne and her squire Podrick Payne to escape Riverrun on a boat. He stays to die fighting for his home, though he admits he'll 'probably make a fool' of himself due to a lack of recent combat experience. A Lannister soldier reports to Jaime that the Blackfish was killed in a fight.
Brynden was known as “The Blackfish,” due to the strained relationship between him and his older brother Hoster. Alongside Barristan Selmy, Brynden showed great heroism during the War of the Ninepenny Kings, a rebellion in the East that threatened the Seven Kingdoms. Though he was present at the Twins for his nephew Edmure's wedding to Roslin Frey, the Blackfish managed to escape before the carnage began. The Tully forces under his leadership recaptured Riverrun from the Freys, but the castle was lost again when Edmure made a separate arrangement with Jaime Lannister. Despite Brienne of Tarth's plea that he join Sansa's fight for Winterfell, he refused to leave and was killed defending Riverrun.