Ser Jaime Lannister is a knight of the Kingsguard, a position he has held for twenty years since he was a teenager, the youngest Kingsguard ever. He was appointed to the position by the Mad King, Aerys II Targaryen.the son of Tywin Lannister, twin brother of Queen Cersei Lannister, and older brother of Tyrion Lannister. Previously he served in the Kingsguard of Aerys II Targaryen and, infamously, he betrayed and killed Aerys during the Sack of King's Landing, earning him the sobriquet "The Kingslayer". Jaime is involved in an incestuous sexual relationship with Cersei, and, unknown to most, is the biological father of her three children, Joffrey, Myrcella and Tommen.