Brynden Tully is the younger brother of Hoster Tully. Hoster is the Lord of Riverrun and the head of House Tully. Brynden is a respected knight and formidable battle commander. He is the uncle of Catelyn Stark, Edmure Tully and Lysa Arryn.
Brynden has often argued with his older brother Hoster, particularly over the fact that Brynden has never married, turning down several potential marriage alliances which may have aided House Tully. As a result, Brynden took up the nickname "the Blackfish", because the sigil of House Tully is a fish, and he is considered the "black sheep" of the family, hence, he is the "black fish". Despite his disagreements with his brother because he never married, Brynden is very devoted to his family, and a revered battlefield commander.
Behind the scenes
He was announced as appearing in Game of Thrones and was expected to debut in the second season based on comments by George R.R. Martin. He was not cast for the first and second seasons, however, a press release confirmed he would be cast in Season 3. He is played by Clive Russell.
In the books
In the A Song of Ice and Fire novels, the Blackfish is a canny and respected warrior. He is tall and clean-shaven, and dons a red and blue Tully cape, like his nephew Edmure. Brynden possessed the distinctive auburn hair of the Tully family in his youth, but it has now gone mostly grey.
Brynden is an experienced battlefield commander. He rose to particular distinction during the War of the Ninepenny Kings which was fought over the Stepstones, in which he fought alongside Barristan Selmy. The young Jaime Lannister highly revered him and was eager to hear of his exploits in the war.
In the novels he is first encountered serving in the Vale of Arryn, where he serves his niece, the Lady Lysa, following the death of her husband, as the Knight of the Gate. After Catelyn asks for his assistance, he agrees to return to the Riverlands and help in the growing struggle against the Lannisters. In the TV series, Brynden's activities in the Vale have been taken over by Ser Vardis Egen.
Along with Edmure, he becomes one of King Robb Stark's most trusted lieutenants, "eyes and ears". Theon Greyjoy references the Blackfish's capacity for battle.
- Brynden Tully at A Wiki of Ice and Fire (MAJOR spoilers from the books).