Little Man With A Big Punch: Al Pratt, The Original Atom
Who is the Atom? If you said Ray Palmer, or Ryan Choi, or "that guy from the Justice League who changes size," or Brandon Routh on Legends of Tomorrow, you certainly wouldn't be wrong.
But there was an Atom who came before all of them. His name was Al Pratt, and while he's not the most well-remembered Golden Age hero, he was an early version of a far-reaching archetype: the unstoppably tough undersized scrapper.