Marlin Guppy is the inventor and owner behind Gadgets By Guppy, a stall on the Kingfish Pier in 1899 Bluff City. He went to an inventor academy, and has never stolen anything.
He is the creator of the Immortal Doll (as well as less impressive inventions such as a sun-shield to clip to the back of your deck chair, a new way to make a deck chair fold, a reverse periscope that lets you see fish underwater, and a "sticky net" used for getting fish out of the deep ocean). His creation disturbs him deeply.