Tyrion Lannister is a member of House Lannister and is the third and youngest child of Lord Tywin Lannister and the late Joanna Lannister. His older siblings are Cersei Lannister, the queen of King Robert Baratheon, and Ser Jaime Lannister, a knight of Robert's Kingsguard.
Tyrion is a dwarf; because of this he is sometimes mockingly called the Imp and the Halfman.
Tyrion was born a dwarf - a horrid state of affairs in Westeros, where such unfortunates were seen as monsters and malformed. The added tragedy of his birth killing his beloved mother set him upon a course of misery that would follow him for most of his years.
He was imprisoned by Lady Catelyn Tully based on her suspicions that he had a hand in the attempted murder of her son, Bran Stark, but was released after his champion was victorious in a trial by combat. Both men leave the Eyrie on the dangerous High Road, and along the way they are surrounded by men of the mountain clans, led by Shagga. Tyrion uses his quick wits and words to win over the clansmen by promising them weapons, armor, and glory. The group rides out of the mountains, eventually reaching the Lannister host led by his father, Lord Tywin, who invaded the Riverlands following Tyrion’s capture.
After the Battle of the Green Fork, Tyrion is sent to King's Landing to act as Hand of the King. He is there for only a short while before Renly Baratheon's host arrives, putting the city under siege. Despite his efforts to prepare the city, or organize a better defense, King's Landing falls to House Baratheon, and Tyrion's father, Tywin, is killed in the fighting. Renly enters the city triumphant, and chooses to exile Tyrion - and his niece and nephew - rather than executing him.