Third-born son of Lord Gerold Lannister and Lady Rohanne of House Webber, born around 220 AC at Casterly Rock and made heir to the Rock only by the deaths of his elder twin brothers — Ser Tywald in the Peake Uprising in 233 AC, and Tion at the Battle of Wendwater Bridge in the Fourth Blackfyre Rebellion three years after. He was squired as a boy but never won his spurs, loved tourneys but never tilted in one, and was wed in 235 AC to Lady Jeyne Marbrand of Ashemark who gave him five surviving children: Tywin, Kevan, Genna, Tygett, and Gerion. His widowed good-sister Ellyn Reyne is said to have tried to seduce him from his marriage bed almost as soon as Tion was buried, and when Tytos failed of his manhood for fear of her and confessed it to Jeyne, the lady of his house went to Lord Gerold, who wedded Ellyn quickly off to his aging bannerman Lord Walderan Tarbeck — a grievance the Reynes would carry into the generation that came after, and that the Reyne-Tarbeck revolt of his son's days would balance.
In 244 AC he succeeded his father as Lord of Casterly Rock, and the realm soon learned that what had been ferocious in old Lord Gerold's lion was toothless in his heir's: the lord's loans were never repaid, his bannermen ignored his summons, and the lords of Faircastle, Castamere, and Tarbeck Hall built their power upon the silence of his answer. His own guests called the mockery they made of him twisting the lion's tail, and the western lords took to japing of toothless lions as the fashion of the age. After Lady Jeyne went to her grave he gave himself entirely to drink, cheese-cake, and a string of mistresses upon whom he settled the keepings of his household, while his sons returning from the War of the Ninepenny Kings undertook the rebuilding of the house's name by sword and ledger. He died in 267 AC of a burst heart climbing the steps of the Rock to visit his second mistress, and was succeeded by Tywin, who forced the woman on a walk of atonement naked through Lannisport before banishing her, and who never afterwards forgave the realm a laugh at a Lannister.