Tywin Lannister

Lord Tywin Lannister is the head of the powerful Lannister family, one of the richest and most influential families in Westeros. He is a widower with three children, Jaime, Cersei and Tyrion, and a younger brother, Kevan.

The actor playing Tyrion has not been announced so far, but George R.R. Martin confirmed he will be in the series, debuting around episode 8 of the first season.

In the books
In the Song of Ice and Fire novels, Tywin is a ruthless, pragmatic leader and a formidable general and strategist, although he prefers to orchestrate events from behind the scenes rather than leading from the front. His father was a weak ruler who was mocked by many of his vassals. When Tywin became Lord, he destroyed two of these lesser houses, cowing the rest into respect and obedience. He was the Hand of the King under King Aerys II Targaryen for twenty years before a series of insults saw him resign the position. When Robert's Rebellion erupted, Tywin took no part. When it became clear that the rebels would be victorious, Tywin betrayed Aerys by sending his army to sack King's Landing, delivering Robert Baratheon his final victory of the war. Tywin pledged fealty to Robert in the aftermath of the conflict, and Robert agreed to marry Tywin's daughter Cersei.

Tywin is proud of his son Jaime, a great warrior, but loathes his youngest son Tyrion, blamining him for the death of Tywin's wife, Joanna, in childbirth.