 The names for all three atomic bomb designs—Fat Man, Thin Man, and Little Boy—were chosen by Serber based on their shapes.Thin Man was a long device, and its name came from the Dashiell Hammett detective novel and series of movies of the same name.The Fat Man was round and fat, and was named after Sydney Greenstreet's "Kasper Gutman" character in "The Maltese Falcon".