Dragon Ball Z picks up five years after the end of the Dragon Ball anime, with Goku as a young adult and father to his son, Gohan. A humanoid alien named Raditz arrives on Earth in a spacecraft and tracks down Goku, revealing to him that he is his long-lost big brother and that they are members of a nearly extinct extraterrestrial race called the Saiyans (サイヤ人, Saiya-jin). The Saiyans had sent Goku (originally named "Kakarot") to Earth as an infant to conquer the planet for them, but he suffered a traumatic brain injury soon after his arrival and lost all memory of his mission, as well as his blood-thirsty Saiyan nature. Goku refuses to help Raditz continue the mission, which results in Raditz kidnapping Gohan. Goku decides to team up with his former enemy Piccolo in order to defeat Raditz and save his son, while sacrificing his own life in the process. In the afterlife, Goku trains under the ruler of the North Galaxy, King Kai, and is taught the Kaio-ken (界王拳) and Spirit Bomb (also known as the Genki Dama|元気玉) techniques, before being revived by the Dragon Balls a year later in order to save the Earth from Raditz' comrades; Nappa and the Saiyan prince Vegeta, who arrive before Goku returns. Piccolo is killed during the battle, along with Goku's allies Yamcha, Tien Shinhan and Chiaotzu (with Chiaotzu sacrificing himself to save Tien), and the Dragon Balls cease to exist because of Piccolo's death. After Goku finally arrives at the battlefield, he avenges his fallen friends by defeating Nappa with his new level of power. Vegeta himself enters into the battle with Goku, but is ultimately also defeated thanks to the efforts of Gohan and Goku's other surviving allies Krillin and Yajirobe. At Goku's request, they spare Vegeta's life and allow him to escape Earth.