As a young adult, Goku meets his older brother Raditz, who tells him that they come from a race of extraterrestrials called Saiyans. The Saiyans had sent Goku to Earth as an infant to conquer the planet for them, but he suffered a severe head injury soon after his arrival and lost all memory of his mission. Goku refuses to help Raditz continue the mission, after which he begins to encounter other enemies from space, most notably the Saiyan prince Vegeta, who becomes his rival and, eventually, his ally as well. He later encounters Frieza, the galactic tyrant responsible for the destruction of the Saiyan race, whose actions cause Goku to transform into a legendary Super Saiyan. After an epic battle on the planet Namek, Goku defeats Frieza, avenging the lives of millions across the universe.[2] Four years later, a group of androids from the former Red Ribbon Army appear, seeking revenge against Goku. During this time, an evil life form called Cell emerges and, after absorbing two of the androids to increase his power, holds his own martial arts tournament to decide the fate of the Earth, but is eventually defeated by Goku's first child Son Gohan. Seven years later, Goku is drawn into another battle for the universe against an extraterrestrial named Majin Buu. Joined by Vegeta and Gohan, Goku succeeds in destroying the evil half of Buu and the good half of Buu settles down with them. Ten years later, at another World Martial Arts Tournament, Goku meets the evil Buu's human reincarnation, Uub. At the end of the series, Goku takes Uub away on a journey to train him as the Earth's next defender.[3]