Aerys II Targaryen (243AC - 283AC), Successor of Jaehaerys II and King of the Seven Kingdoms (262AC - 283AC). Son of Jaehaerys II. Known as "The Mad King". Although his reign began with peace and prosperity, he descended into madness following his capture and imprisonment during the Defiance of Duskendale. He was overthrown by Robert Baratheon and Eddard Stark during Robert's Rebellion. The last of the Targaryen Kings in Westeros and father of Rhaegar, Viserys and Daenerys.
The powerful and wealthy patriarch of house Lannister, Tywin is Lord of Casterly Rock and Warden of the West. And is fear throughout Westeros. He is accustomed to command and control, having secreted as the Mad King Aerys Targaryen's Hand for 20 years - before Tywin turned on Aerys and sacked King's Landing.