Grandpa Son Gohan became the adoptive father and grandfather of Son Goku when he found him near the landing site of his space ship when he was an infant. Gohan was taught martial arts by Muten-Roshi and passed on his knowledge to Goku. Gohan warned Goku to never look at a full moon and to stay indoors on nights of one - implying that he had already transformed before and Gohan managed to survive the first time. He followed his advice for sometime until one night when Goku stepped outside to relieve himself; he then glanced at it, transformed into an Oozaru and killed Gohan by stomping on him. From that time on, Goku believed that Gohan's soul was in the Four-Star Dragon Ball.
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