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.
He then only appears in flashbacks for the rest of the series. Grandpa Gohan is a playable character in Dragon Ball: Advanced Adventure and Dragon Ball Z: Budokai Tenkaichi 2.
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