First-born son of Lord Tywin Lannister and the Lady Joanna, born minutes after his twin sister Cersei in 266 AC at Casterly Rock and holding her foot as he came into the world. The two were inseparable as children, dressed in each other's clothes for whole days, climbed into the cages where his grandsire Tytos had kept his lions, and shared a bed long after they had been told they should not, until a servant came on them at play and the lady-mother shifted his chamber to the other side of the Rock. Joanna died in 273 AC bearing Tyrion, and the love Jaime gave his little brother thereafter set him apart from a father and a sister who only despised the boy for being born. He was sent at eleven to squire for Lord Sumner Crakehall, won his first melee at thirteen, and at fifteen rode in the Kingswood with the host that put down the Kingswood Brotherhood, where he saved his lord from Big Belly Ben and crossed swords with the Smiling Knight; for that day's work Ser Arthur Dayne knighted him with Dawn upon his shoulder.
In 281 AC Aerys II raised the fifteen-year-old to the Kingsguard at the great tourney at Harrenhal — the youngest knight ever to wear the white cloak, and a deliberate insult to his father, who pleaded ill, set down his Hand's chain, and rode home to Casterly Rock taking Cersei with him. For two years Ser Jaime stood at the foot of the Iron Throne and watched the king burn men: Lord Rickard Stark roasting in his armour, Brandon Stark strangling himself reaching for the sword to save his father, Lord Qarlton Chelsted afire for throwing his chain at the throne when he learned of the pyromancers' caches of wildfire seeded beneath the city. He stood guard outside the queen's chambers the night the king grew hot from the burning and forced himself on his sister Rhaella, and when Jaime spoke of it his sworn brother Jonothor Darry told him they were sworn to guard the queen, but not from him. He begged Prince Rhaegar to take him to the Trident in another knight's place and the prince refused, charging him instead with the safe-keeping of Princess Elia and her children; that charge he was not able to keep.
When Lord Tywin's host was let through the gates at Grand Maester Pycelle's urging and the Sack began, the king sent for Jaime and commanded him bring his father's head, while the pyromancer Rossart hurried out a postern dressed as a common soldier with orders to fire the city in its caches. Jaime ran Rossart down in the street and went up to the throne room with the blood still on his sword, and when the king cried for Tywin's head he hauled the king down off the steps of the Iron Throne and opened his throat with a single cut, that no other pyromancer might be sent to light the fires; afterwards he sat the throne himself with his golden sword across his knees and was found there by Lord Eddard Stark, to whom he gave it up calling it an uncomfortable seat. He was pardoned at the wedding of his sister to King Robert on Lord Arryn's counsel, and the realm called him Kingslayer from that day forward, a name he has carried through three children got upon his own twin under a Baratheon roof — Joffrey, Myrcella, and Tommen — and a Kingsguard's white he has worn through every reign since.