Originally Goku was sent to Earth as a baby in order for him to grow up and destroy it. However, when Goku was a child he hit his head on something and became Good. Years later when Goku had grown up, his brother Raditz arrived on Earth, wondering why Goku had not yet destroyed it. When Raditz confronts Goku, he tells Goku that he is a Saiyan from the planet Vegeta. He then attempts to convince Goku to join him in destroying the planet. When Goku refuses, Raditz kidnaps Gohan, in order to bribe Goku into cooperation.
Goku and Piccolo then band together to face their common enemy, Raditz. Their power was not enough to defeat the Saiyan however, and it took the rage of the young Gohan to inflict any damage at all. After Gohan had cracked Raditz's armour, Goku held Raditz in a death lock, allowing Piccolo to fire his Demon Ray through Raditz's chest, and through Goku (killing them both).