Despite his obvious importance, author Eiichiro Oda has only provided a few details regarding Joy Boy and the effect that he had on the history of One Piece. However, using these facts, it is possible to start to piece together a profile for the show's forgotten legend.
As important as Joy Boy is to the events of One Piece, it has been clear since the very first episode that this series revolves around one person - Monkey D. Luffy. He is destined to become King of Pirates, but as is becoming increasingly clear, his future may also involve assuming Joy Boy's mantle as well.
Joy Boy predicted that an individual would return in 800 years to help Fish-Man Island where he couldn't, open the borders of Wano, and uncover the secrets of Laugh Tale. Luffy is well on his way to doing all three. Also, while Luffy used his newly-discovered Gear 5 form to defeat Kaido, Zunesha bluntly stated that Luffy's actions marked the return of Joy Boy. Considering this, it seems clear that the Straw Hat Pirates' captain is the person destined to carry his torch.