Lord Tyrion Lannister is the youngest child of Lord Tywin Lannister and younger brother of Cersei and Jaime Lannister. A dwarf, he uses his wit and intellect to overcome the prejudice he faces.
His abduction by Catelyn Stark for a crime he did not commit serves as one of the catalysts of the War of the Five Kings. After escaping his captors, Tyrion is appointed by his father as acting Hand of the King to Joffrey Baratheon and successfully defends King's Landing against Stannis Baratheon, after which he is stripped of his power, demoted to Master of Coin and eventually framed for Joffrey's murder. After his champion, Oberyn Martell, dies in Tyrion's trial by combat, Tyrion flees to Essos with help from Jaime after murdering his father, whereupon he is captured by Jorah Mormont and taken to Daenerys Targaryen in Meereen, who decides to enlist his help in reclaiming the Iron Throne. For his loyalty and service, Tyrion is named as Daenerys's Hand before they set sail for Westeros with Daenerys's new army.
(Source GOT wiki)