Gerion Lannister was the youngest brother of Tywin Lannister who travelled to the ruins of Valyria in search of the lost Valyrian sword Brightroar, but did not return.
He was said to be a man quick to laugh and had a gift for making others laugh. His mother, Jeynne Marbrand, died when he was only a month old. Tyrion and Jaime often refer to him as their favorite uncle. He is remembered fondly by the former for rewarding and supporting Tyrion when the dwarf recited historical facts memorized by heart or cartwheeled across the supper table in Casterly Rock's great hall.
Like his brothers, Kevan and Tygett, Gerion was overshadowed by their older brother Tywin Lannister. While Kevan built up a life near Tywin and Tygett tried to be independent, Gerion mocked this "game" and made jokes.
Almost a decade passed after his ship the Laughing Lion left Lannisport but Gerion never returned. Tywin Lannister sent men to look for his lost brother and they traced him as far as Volantis, where half his crew had deserted him because of his intent to sail into the Smoking Sea. He had to buy slaves to replace them.