From A Wiki of Ice and Fire
|Title|| Lord of Casterly Rock|
Warden of the West
Lord of the Westerlands
|Book(s)||The Princess and the Queen|
Jason Lannister was Lord of Casterly Rock during the reign of King Viserys I and Aegon II. During the civil war known as the Dance of the Dragons he was loyal to King Aegon and the greens. He has a younger twin brother, Tyland Lannister, who was the master of coin during the Dance of the Dragons.