<P> Five years later , Goku meets his evil older brother Raditz and sacrifices himself to defeat Raditz after he learns about his heritage . Goku comes from a race of extraterrestrials called Saiyans , himself having been sent from their home planet to prepare Earth for sale on the intergalactic market by destroying all its life . While Grandpa Gohan was taking care of him , Goku suffered a severe head injury and forgets his mission to conquer Earth . In order to fight the Saiyans invading Earth , Goku trains with King Kai in the afterlife . He teaches Goku the Kaiō - ken ( 界 王 拳 , lit . `` World King Fist '' ) , which multiplies his ki and strength for an instant , but with possible strain to the body . It is also from King Kai that Goku learns his most powerful attack : the Genki - Dama ( 元気 玉 , lit . `` Energy Sphere '' , renamed `` Spirit Bomb '' in Funimation 's dub ) , an energy sphere created by gathering ki from surrounding animals , nature and humans . After being revived by the Dragon Balls , Goku faces off with the Saiyan prince Vegeta , who eventually becomes another ally . On his journey to Planet Namek in order to aid his friends in gathering the Namekian Dragon Balls to revive the ones killed by the Saiyans , Goku fights the galactic tyrant Frieza , who destroyed the Saiyans ' home planet and nearly the entire race . During his epic battle with Frieza , Goku becomes the first Saiyan in a thousand years to transform into a fabled Super Saiyan . </P>
when did goku first go super saiyan 4
During his epic battle with Frieza