Gaimon is a former pirate who years ago while searching for treasure fell off a cliff into an empty treasure chest. Over the next twenty years the treasure chest became a part of his body
and could not be removed without killing him.
He's hostile to any one who either wants to harm the local animals on the island or search for hidden treasure. If the visitors do neither he's quite friendly.
In the English dub of the One Piece anime by Odex Gaimon was voiced by Joe Murray.
In the English dub of the One Piece anime by 4Kids Entertainment he was voiced by J. David Brimmer.
In the English dub of the One Piece anime by Funimation Entertainment he is voiced by Jonathan Osbourne.