The Atom is a Golden Age superhero who made his debut in 1940 in the pages of All-American comics. His secret identity is college student Al Pratt. Unlike his later counterpart in the DC Universe, the character didn’t have any super powers; he was a short (5’1″) skinny guy who decided to go all Charles Atlas and become muscular in an attempt to impress a woman he had a crush on. Once his training program succeeded, he decided to put those muscles to use and put on a costume and fought crime. That’s it, he was just a short muscular guy who liked punching crooks in the face. This was good enough for the Justice Society, who made him a member. Eventually, in 1948, Al Pratt acquired powers somehow and got a different costume, but I prefer the original version.