Joy Boy was an extremely relevant figure of the Void Century who played an important role in the history of Fish-Man Island and left behind a certain item of unimaginable value on the last island of the Grand Line. He was first mentioned on the Ryugu Poneglyph read by Nico Robin while at the Sea Forest. Gol D. Roger declared that he wished the two could have lived during the same period upon learning the true history on Laugh Tale.
Judging by Kaido musing whether or not Luffy could "be Joy Boy", as well as Oden expecting Joy Boy's reappearance 900 years after his last known appearance (the apology on the Poneglyph), it is unknown if "Joy Boy" is the name of a single person or a title that can be inherited by others.
Around 900 years ago, the residents of Fish-Man Island made a promise to a great man known as Joy Boy. He attempted to raise Noah with Poseidon's aid, but he broke his promise to Fish-Man Island. However, Fish-Man Island promised that they would keep Noah safe until a certain day came. Joy Boy left a letter in the form of poneglyph to Poseidon, apologizing for breaking his end of the bargain.
Fish-Man Island's half of the promise was almost broken during the events of the Fish-Man Island Arc, when Monkey D. Luffy was asked to protect the island no matter what the cost, even if it meant that Noah had to be destroyed in the process. Before Luffy could destroy the ship completely, Noah's fall was stopped by a group of Sea Kings that were summoned unknowingly by Shirahoshi, thus saving Fish-Man Island and maintaining the nation's promise to Joy Boy. However, the ship was still heavily damaged. The Sea Kings then took the ship to the Sea Forest, where they planned to fix it.
- Joy Boy made a promise with the residents of Fish-Man Island 900 years ago, but since the Poneglyphs were invented by the Kozuki Family 800 years ago, his letter of apology was written at least a century later. If the letter was written by Joy Boy himself, he had a lifespan of at least 100 years.
- Oden wished for Wano Country to open its borders before the day Joy Boy finally reappears.
- Kaido stated that Luffy "couldn't be Joy Boy either", after defeating him a second time.
- One Piece Manga and Anime — Vol. 64 Chapter 628 and Episode 548, Nico Robin reads about Joy Boy on the Ryugu Poneglyph.
- One Piece Manga and Anime — Vol. 66 Chapter 649 (p. 16-18) and Episode 569, Neptune explains to Robin who Joy Boy was.
- One Piece Manga and Anime — Vol. 96 Chapter 967 (p. 17-19) and Episode 968, The Roger Pirates find Joy Boy's treasure on Laugh Tale.
- One Piece Manga and Anime — Vol. 96 Chapter 968 (p. 8) and Episode 969, Oden states his desire for the future of Wano.
- One Piece Manga — Chapter 1014 (p. 3), Kaido states that Luffy could not "be Joy Boy" either.
- One Piece Manga and Anime — Vol. 66 Chapter 647 (p. 11-19) and Episode 567.
- One Piece Manga and Anime — Vol. 66 Chapter 648 (p. 2-7) and Episode 568, The Sea Kings stop and take Noah to be repaired.