Piccolo is the son/reincarnated form of the Demon King Piccolo, who had been the evil expunged from Kami, the Guardian of Earth. read more
He was evil because he was the son of King Piccolo who was already a villain in the original Dragon Ball Series. Being around Goku and the others as well as seeing his own people and planet fall victim to other villains eventually led him to become a good guy. read more