Luffy's relatives are still shrouded in mystery. Luffy meets his other older brother, Portgas D. Ace, in Alabasta. Ace, a.k.a. "Fire Fist" Ace, whom has eaten the Mera Mera (Fire Fire, "Flare Flare" in the English dub) Fruit and thus can manipulate fire at will. After Luffy and his crew land on Longring Longland, Admiral Aokiji relates meeting Luffy's grandfather. Though no details about him were given, it was the only time Luffy has ever appeared genuinely afraid. In the original version planned, Luffy's grandfather was the one shown giving Luffy his straw hat. It is speculated by fans that Luffy's grandfather is either Gol D. Roger or Jaguar D. Saul, although Saul is a giant. There is also evidence that Luffy's middle initial "D." is a key element in uncovering the identity of his relatives. He might also be related to Marshall D. Teach (Blackbeard). from Wiki, this is basically what u want