In an interview, series creator Eiichiro Oda revealed his favorite character in One Piece. While he is a big fan of Luffy and most of the Straw Hat Pirates, his most favorite one isn’t any of them. Oda revealed in an interview with Dragon Ball’s creator Akira Toriyama that his favorite character is Gaimon.
I like Luffy. But the character I like the most is Gaimon.
It’s hard to think of anyone better than him. Just a man who has been stuck in a treasure box for 20 years. I think that was an amazing setup myself.
Gaimon is a former pirate who currently lives as a hermit on the Island of Rare Animals.
In the manga, Gaimon’s debut is a relatively low-key event taking place between the between the Orange Town Arc and the Syrup Village Arc, with Luffy and Nami being the only Straw Hat Pirates he meets (as Zoro was too battle-exhausted to go ashore). The anime places Gaimon’s debut between the Syrup Village Arc and the Baratie Arc, incorporating both Zoro and Usopp into the meeting and somewhat expanding the overall story.
As a young man, Gaimon was a stereotypically greedy pirate, caring about little more than plunder. This greed slowly eroded (though never completely erased) by his decades of solitude on the Island of Rare Animals, causing him to prize peace and companionship more than any material wealth.
Although he tried to attack the Straw Hat Pirates at first, he ends up making friends with them after telling them about his past, and they tried to help him get the treasure chests he had been wishing for. However, with the chests empty, Luffy asked him to join his crew, but Gaimon declined the invitation to stay with the animals.