Son Gohen is goku and Chi-Chi's third son, he would have been on earth with the other heros of earth but because he was born with a power level of nine hundred and ninty nine billion the Kais like King Kai thought it best to raise him themselves so that he wouldn't have a power outburst and kill a lot of people, the Kai's know one thing that is very important, Gohen is the legendary mystic Super Saiyan and is both full Saiyan and Human with mystical powers making it that he is unknown to all Z Fighters and his own parents.