Gaimon

Gaimon (ガイモン) is a former pirate who lives as a hermit on the Island of Rare Animals. He first appeared in the manga between Buggy the Clown arc and the Captain Kuro arc, in the anime he appeared in between the Captain Kuro arc and the Baratie arc.

Past Story
Gaimon's life changed when he was searching for treasure on the island as part of an unnamed pirate crew. While searching, he fell from a high cliff and directly into an empty treasure chest at the bottom. His crew, considering him a lost cause, leave Gaimon stranded on the island.

The treasure chest becomes his body and cannot be removed, however, he can still use his hands, head and feet. Because Gaimon shrank to fit the size of the small chest, he can no longer scale the cliff to the treasure. He managed to befriend the strange animals on the island, and develops a close bond with them. To protect his treasure and his 'nakama', he does not allow any visitors on his island. If any sailors come ashore there, he hides and tells them to leave in a spooky voice, claiming to be God. If this fails, he takes the more direct route of shooting them with a pistol (which he apparently keeps hidden inside his afro).

Present Story
Twenty years after he was first stranded, Monkey D. Luffy and his crew arrive on the island. They survive his deterrent tactics, and, after he realises that they aren't there to steal from him, they become friends. However, when Luffy finally gets to the top of the cliff, Gaimon realized that the treasure chests were empty too and he had been protecting a nonexistent "treasure" for 20 years. Then, he considers the animals as his treasures, and vows to protect them.

Chibi Buggy eventually meets, and befriends, Gaimon in the "Special Cover Miniseries".

Trivia

 * Eiichirō Oda has stated that Gaimon is his favorite character to draw.