Long before Kick-Ass and Hit-Girl, long before Super, there was Hero At Large, the original story of a regular guy who becomes a superhero. And gets his ass kicked massively.
1980's Hero At Large is actually a pretty fun movie, with that goofy sense of humor that so many late 1970s-early 1980s comedies had. And it's ahead of its time, in some ways, in deconstructing the idea of superheroes as celebrities and media phenomenons.
Ritter plays Steve, a struggling actor who gets a gig dressing up as a superhero, Captain Avenger, to promote a new movie. The funniest bit is actually early on, when he's doing a promotional appearance and starts getting hassled by teenagers who keep asking if they can feel his muscle. And then another actor who's appearing as Captain Avenger confesses that he's not particularly tough in his ass:
Soon after that, Steve is in a small grocery store run by a stereotypical Jewish couple, when some punks try to rob it. Steve is still wearing his Captain Avenger costume under his coat, so he decides on the spur of the moment to stop the robbery as Captain Avenger. This leads to a media frenzy about the vigilante dressed as Captain Avenger who saved the nice old couple, and soon everybody is speculating about when the real-life Captain Avenger will appear next. The more the media obsesses about his crime-fighting career, the more Steve feels like he should keep doing it. And that, in turn, fuels the media frenzy. Soon, the media is driving Steve to go further and further.
And then some sleazy promoter/political operative types decide to have Steve stage some fake crime-fighting in public, so they can use Steve to promote their candidate for mayor. And Steve's quest for fame starts to clash with his genuine desire to be a hero — it's not a bad treatment of the themes that superhero comics and movies have spent the succeeding few decades exploring.
[IMDB, thanks to James Gunn for clueing us in to this film!]