Tyrion is the brother of twins Jaime and Cersei Lannister, the latter of whom is married to King Robert Baratheon. Tyrion is well-read and known for drinking, and his father favors Jaime over him. The Lannister family often has a rocky relationship with that of the Starks, and Tyrion also comes to view them as the enemy after the family causes him to be put on trial for the death of the Hand of the King before Ned Stark and for attempted murder of one of the Stark children, Bran. After hearing about Joffrey's unexpected order to behead Ned, Tyrion's father decides that someone must keep the young king in line and sends Tyrion to serve as the new Hand of the King.

Courtesy of HBO