Stupendous Man is a recurring character in Calvin and Hobbes. He is one of Calvin's many alter egos and an attempted superhero by Calvin. Calvin puts on a red mask and cape which his mom made him, and pretends that other people (mostly those who give him trouble) are villains or monsters. When Stupendous Man's antics get him in trouble, he takes off the costume, and reverts to "mild-mannered millionaire playboy Calvin" (a mashup of Bruce Wayne, the secret identity of Batman, and Clark Kent, the secret identity of Superman).
Stupendous Man is Calvin's second most frequent alter ego, although Calvin admits Stupendous Man has only won "moral victories", not physical ones. Stupendous Man is Calvin's most powerful alter ego, achieving such feats as flying a telescope lens into the atmosphere and turning time back a day. However, he uses these vast powers for mundane ends, either against supervillains (such as his Mom or his teacher) that Stupendous Man cannot defeat or on ultimately futile plans such as getting mild-mannered Calvin another day out of school.