Ser Brynden Tully is a famous knight, who’s fought in half a hundred battles and skirmishes since he first won renown during the War of the Ninepenny Kings. He is also famous for his quarrels with his elder brother, Lord Tully, on topics such as his finally marrying. Ser Brynden always refused, until one day his brother called him the black sheep of the family—ever since, he took the black trout as his sigil, and became known as the Blackfish. Their last argument was shortly following the wedding of his nieces to Lords Stark and Arryn, when he revealed that Lord Arryn had offered to give him the office of Knight of the Bloody Gate; Lord Hoster refused to speak with Brynden after that. They have been estranged since.
Clive Russel doesn’t quite have the thick brows of the Blackfish, but otherwise he seems pretty close.