Gohan (that was Goku's grandfather's name) is the son of Goku and Chichi and he obviously has the Saiyin blood in him. When Gohan gets angry, his power level sky-rockets and even when he hadn't undergone any training, it shot up to 1,400. Gohan recieved his first serious martial arts training from Piccolo through some very tough training which required him to survive by himself in the wild and fight against Piccolo. This training made Gohan quite strong and was the first step to revealing Gohan's hidden powers. Once Gohan reaches his adolescent years, all he has to do is get angry enough, and he can defeat any foe. Gohan is also a great fan of Piccolo and Gohan is pretty much Piccolo's only "friend."
