Gorou Kanzaki

Known mainly as the grandfather of Jin he lived in the slums with Jin disguising himself with a long beard in a house made of wooden planks. His wish was that Jin could grow up as a human not as Zet or a player. Through deception he was able to make Jin lose all of his powers as Zet to save him from the clutches of Amagi Corps. His plan failed however when medicines were created to aid Jin turn into Zet chapter 67. Source: Wikipedia