system
Given the following post, respond as if you're commenting on Reddit:
human
[GAME OF THRONES] who ruled over The Westerlands whilst Tywin served as hand of the king?

The show says he served for 20 years as hand so who ruled The Westerlands in his stead? Was it Kevan? And if so, who took over when Kevan became hand?
gpt
In title, it was still Tywin Lannister though he probably relegated the day-to-day operations to his brother, Kevan (much in the same way Tyrion operate as Hand in Tywin's stead). When Tywin died the title *Warden of the West* was bestowed upon Daven Lannister and Cersei Lannister became *Lady of Casterly Rock* and head of the Lannister family.