Petyr Baelish
After the royal party arrives at Winterfell, Catelyn receives a letter from her sister Lysa Arryn stating that the Lannisters had killed her husband Jon Arryn, the king's 'Hand' (second-in-command). King Robert Baratheon persuades Eddard to take his place. When her son Bran is injured and goes into a coma, she sits by his bed until they are attacked by an assassin who has come to kill Bran. Catelyn is wounded in the attack, and travels to King's Landing to warn Eddard after recovering. There, her childhood companion Petyr Baelish tells her that the dagger used in the attack belongs to Tyrion Lannister. On her way back to Winterfell, she takes Tyrion to her sister at the Eyrie for trial, where Tyrion escapes execution by demanding and winning a trial by combat. After the news of Eddard's execution by order of King Joffrey reaches Catelyn, she argues for peace, but is overruled by the newly crowned King Robb and his bannermen.