Dissatisfaction with the Mad King spread among several noble houses ... Before that could happen, Jaime Lannister betrayed his oath as a member of the Kingsguard and assassinated the king.
Game of Thrones fans know Jaime Lannister as the "Kingslayer," but he went on to become king of Westeros in Martin's first Song of Ice and Fire outline. Tyrion would have been responsible for ...