Officially Hand of the King to his grandson Joffrey, Tywin Lannister has yielded the position to his son Tyrion while he wages war against Robb Stark. As Hand to Aerys Targaryen and the richest man in Westeros, Tywin was considered a threat by the Mad King. Although now grown, Tywin's children are still in awe of him and defer to his counsel.
"Probably the most powerful man in the Seven Kingdoms. Certainly the richest." — Tyrion Lannister