after watching the theory from The Library of Ohara about Joyboy, I believe that he is Luffy's Ancestor
the name is Joy Boy = Sun God Nika = Sun Go D. Nika
Sun Go = Sun Go Kong = Monkey King
so he is the King of Ancient Kingdom, the King of all Monkey's Family, the king of all D's Family
another trivia : Sun Go = Sunny Go
the name is Joy Boy = Sun God Nika = Sun Go D. Nika
Sun Go = Sun Go Kong = Monkey King
so he is the King of Ancient Kingdom, the King of all Monkey's Family, the king of all D's Family
another trivia : Sun Go = Sunny Go