Though he appears human, it is later revealed that Goku is descended from an alien warrior race known as the Saiyans, who sent him, originally named Kakarrot, to Earth to prepare it for conquest. [ ch. 197 ] Goku sacrifices his life to save the planet from his brother Raditz , [ ch. 205 ] but must quickly get stronger in the afterlife under the tutelage of Kaiō-sama , to save it from the other incoming Saiyans Nappa and Vegeta . He later becomes a Super Saiyan and defeats a powerful tyrant Freeza . This sets the tone of the rest of the series, with each enemy the characters face becoming stronger than the last, requiring them to attain further training. The last battle of the original manga, against Majin Boo , has the entire universe at stake, and as such, has Goku and friends being asked for help from the gods of the universe, the Kaiō-shin .