Brynden Tully
The Blackfish: Hoster's brother, the finest soldier House Tully ever produced, who quarreled with his lord over an unwanted marriage and never took a wife at all.
The fuller tale
Every family has one relative who declines to be arranged, and House Tully’s was Brynden. When his brother Hoster pressed a Redwyne marriage on him one time too many and called him the black goat of the Tully flock, Brynden — a Tully, whose sigil is a fish — corrected the heraldry and wore the insult forever after: the Blackfish, a black trout on his arms and a closed door on the subject of wives. He left Riverrun rather than submit, and the brothers barely spoke for the better part of two decades.
He was, by common consent, the finest soldier his house ever produced. He won his reputation young in the War of the Ninepenny Kings, and spent his self-imposed exile in the Vale in service to House Arryn, where the books make him Knight of the Gate — commander of the Bloody Gate, the mountain door through which no army has ever forced its way. It says something about the man that the Vale, the most defensible country in Westeros, put its one indispensable chokepoint in the keeping of a foreigner.
When the war comes he goes to his great-nephew, and Robb Stark’s improbable unbeaten streak owes as much to the Blackfish as to any wolf dream. He commands the outriders — the eyes of the army — and it is his screening and scouting that let Robb appear where no Lannister expects him, at the Whispering Wood and after. He is also the closest thing the young king has to a grandfather in the field: blunt counsel, no flattery, and a standing willingness to tell a king he is being a fool, which Robb gets from no one else after Catelyn is set aside.
The Red Wedding kills nearly everyone he loves and misses him — in the show by minutes, a step outside at the right moment; in the books entirely, because he had been left behind to hold Riverrun. Either way the result is the same: the last Tully in arms, holding the last Tully castle, with a dead king to mourn and no intention whatsoever of yielding to the people responsible. The Freys demand Riverrun; the Blackfish keeps it, feeds it, and settles in to outlast them out of spite as much as strategy.
His siege is the old world’s last argument. Jaime Lannister comes to end it and gets a parley across the drawbridge that has become quietly famous — the Kingslayer offering terms, and an old man in fish-scale armor declining to pretend that any of it is honorable. Brynden Tully never breaks an oath, never takes the convenient road, and never wins anything by it; he is what Ned Stark might have been with thirty more years and no children to protect, and the tale keeps him around precisely to show what that costs.
The page and the screen
The two tellings split at the Twins. Show-Brynden attends the Red Wedding and survives it by stepping out to find a tree — a black joke the episode plays completely straight — while book-Brynden was never there, having stayed to hold Riverrun as Robb’s warden. The endings diverge just as sharply: the show closes his story at the fall of Riverrun, while the book siege ends with the Blackfish slipping the net entirely, swimming out beneath the Water Gate and vanishing into the riverlands. In the published books he is still at large — an unaccounted-for Tully with a sword, which several characters have cause to find worrying.
Where they stand, season by season
Their fate — if death has found them, it is written here. Open at your peril.
The Blackfish retook Riverrun in the war's ashes and refused every demand to yield it. When the siege broke in, the old knight sent Brienne to safety, drew his sword on the castle he was born in, and died as he chose — fighting.
In the show, the siege of Riverrun ends when Jaime threatens Edmure’s infant son and sends Edmure into the castle to order its surrender as its lawful lord. The garrison obeys; the Blackfish will not. He hurries Brienne and Podrick to a boat, refuses her plea to come north to Sansa — he has a castle to die in, he says, more or less — and is cut down fighting, offscreen, sword in hand in the halls where he was born. The show grants him the death he would have picked from a catalogue.
The books stage the same siege with a different last move: when Edmure yields the castle, the Blackfish is simply not among the prisoners. He escapes by the river that named his house and disappears. As of the published books he is alive, whereabouts unknown — the rare character whose show death has no book counterpart at all, only an empty cell and a furious Frey garrison.