From A Wiki of Ice and Fire
Ser Brynden the Blackfish
Warden of the Southern Marches
Knight of the Gate(formerly)
|Allegiance|| House Tully|
|Book(s)|| A Game of Thrones (Appears)|
A Clash of Kings (Appears)
A Storm of Swords (Appears)
A Feast for Crows (Appears)
A Dance with Dragons (Mentioned)
|Played by||Clive Russell|
|TV series||Season 3|
Ser Brynden Tully, also known as Ser Brynden the Blackfish, is a member of House Tully. A skilled and experienced fighter who made his name during the War of the Ninepenny Kings, he proved invaluable to King Robb Stark as an adviser and captain of the outriders. His personal coat of arms consists of the traditional Tully colors, but with a black fish.
Appearance and Personality
Following the motto of his house, he knows his duty and firmly believes in upholding justice and the bonds of family. A kind man, he was the one to whom the Tully children and the ward Petyr Baelish, would go to first with their problems.
He is tall and lean, with a hoarse, smoky voice. His features are lined and weathered. His once-auburn hair has gone to grey. He has bushy eyebrows and bright blue eyes. See also this collection of images.
As Knight of the Gate, Ser Brynden wore heavy plate and helm, but when commanding Robb's outriders trades this for mail and leather. In either suit of armor, Brynden's cloak is fastened by an obsidian clasp in the shape of a black fish.
Brynden is the younger brother by five years to Lord Hoster Tully. The brothers remained close through their childhood. After squiring for Lord Darry, Brynden was Knighted and during the War of the Ninepenny Kings, he left the Riverlands with many other knights to fight the Band of Nine.
When he returned his relationship with his brother Hoster became strained, after Brynden refused to marry a woman he had chosen for him, to advance the family's fortunes. This led to years of nasty quarrels and estrangement. After one such quarrel with his elder brother, when Lord Hoster called him the "black goat of the Tully herd", Ser Brynden pointed out that their sigil was a fish, so he took the name 'Blackfish,' and changed the Tully emblem to a black trout jumping.
With no reconciliation in sight after Robert's Rebellion, he accompanied his niece Lysa Tully to the Vale of Arryn where he served House Arryn. For his years of loyal service, Lord Jon Arryn named him Knight of the Gate, a position of great honor in the Vale of Arryn.
A Game of Thrones
Ser Brynden meets Catelyn Tully at the Bloody Gate when she arrives after capturing Tyrion Lannister and riding through the Mountains of the Moon. After news of attack of the Lannisters upon the riverlands arrive, Ser Brynden quarrels with Lysa Arryn over her decision to not send aid to Riverrun. He resigns his position as Knight of the Gate and accompanies Catelyn to White Harbor and on to Moat Cailin.
Once Ser Brynden meets up with Robb Stark at Moat Cailin, he quickly becomes a part of Robb's war council and is assigned as leader of the outriders. In that capacity he clashes with Lannister cavalry under command of Ser Addam Marbrand; his repulse of that force allows Robb to cross the Trident undetected. He participates in the Battle of the Whispering Wood, commanding the party that draws Ser Jaime Lannister out of his encampment, and leads the van at the Battle of the Camps.
After lifting the siege of Riverrun and finding his brother Lord Hoster on his deathbed, he chooses to reconcile with him, leaving the past behind.
A Clash of Kings
Brynden helps King Robb plan his expedition into the Westerlands, and on the ride west, leads Robb's scouts. In the Battle of Oxcross he first picks off Lannister sentries before leading the van to crushingly rout the gathering enemy host.
A Storm of Swords
After campaigning with Robb Stark throughout the Westerlands, he returns to Riverrun, where he remains when Robb goes to retake the western North from the ironmen and visit the Twins to attend the wedding of Edmure Tully. In recognition of his military contributions, Robb names him Warden of the Southern Marches. 
A Feast for Crows
After the Red Wedding and the death of Robb Stark, Brynden continues to hold Riverrun in his name, even as other Riverlords surrender and bend the knee to the Iron Throne. Besieged by Lannister and Frey forces, he treats with Ser Ryman Frey but refuses to give up Riverrun or Queen Jeyne, unmoved by Ryman's empty daily threats to hang Edmure.
The Blackfish holds out for several months, until Ser Jaime Lannister came to resolve matters. Brynden parleys with Jaime, but only as an excuse to hear Ser Jaime's reasons for not returning Catelyn's daughters and to see Ser Jaime's stump. 
Before Edmure surrenders the castle to Ser Jaime, Ser Brynden escapes by swimming under the portcullis that had been slightly raised at the Water Gate. He escaped downriver and his current whereabouts are unknown.