Originally there were two Nuclear Men in
Superman IV (1987). Mark played the second Nuclear Man, while the original Nuclear Man was played by British actor
Clive Mantle, who proved to be ineffective and was quickly destroyed by Superman (
Christopher Reeve), with Mark being the improved version reforged from the remains of the first Nuclear Man. All of Mantle's footage and virtually all references to him were cut from the theatrical version of the film, leaving Mark as the only Nuclear Man. The original Nuclear Man was also infatuated with Lacy Warfield (
Mariel Hemingway) and the second Nuclear Man remembered her, which is why he goes after her in the film's climax.
