Joy Boy was a man from the Great Kingdom, born 900 years ago at the beginning of the Void Century. He is also considered to be the first pirate in history. As a figure of immense relevance during the Void Century, Joy Boy played a crucial role in the history of Fish-Man Island and left behind an artifact of immeasurable value on the final island of the Grand Line.
One of the key elements of Joy Boy's story is his connection to the Ancient Weapons, particularly the weapon known as Poseidon. The Poneglyph found on Fish-Man Island reveals that Joy Boy intended to use Poseidon to fulfill his promise, which likely involved moving the Fish-Man Island's inhabitants to the surface.
Joy Boy's unfulfilled promise is a central theme in the series, and many fans speculate that it is closely tied to the "Will of D.", a mysterious concept referring to those who carry the initial "D" in their names. The Will of D. is often associated with bringing about significant change or revolution in the world.
As the story of One Piece progresses, the role of JoyBoy becomes increasingly significant. Gol D. Roger, the Pirate King, discovered the truth about Joy Boy and his promise when he reached Laugh Tale, the final island of the Grand Line. Roger and his crew were so moved by what they learned that they named the island "Laugh Tale", reflecting the irony and joy of the revelations they uncovered.