Doppy is an alien from the series Planet Sheen. He lives on Planet Zeenu, and looks and sounds a lot like Carl. Just like Carl, Doppy can be nervous, cowardly and cautious. However, he is more sensible than his extremely overprotective parents. Unlike Carl, Sheen never tries to scare Doppy or yells at him.
Carl was supposed to appear in the series, in which it would've been about him and Sheen stealing Jimmy's rocket, but a Nickelodeon executive wanted it to be just about Sheen and so, Doppy was made.