1912 - Al Pratt is born.
1927 - 15-year-old Al begins bodybuilding & boxing, tired of being small & skinny.
1933 - 21-year-old Al begins working as a chemist.
1936 - 24-year-old Al first dons a strong man costume to fight crime as the Atom.
1939 - WW2 begins. 27-year-old Al starts working in the Manhattan Project in Nevada.
1942 - 30-year-old Al absorbs the latent energy of an experimental nuclear device and gains Atomic Powers.
1945 - WW2 ends.
1951 - The Justice Society is trapped in Ragnarok, including 39-year-old Al, who dies while escaping.
While most of the Golden Age heroes of the Justice Society have a very specific innovation about them that makes them stand out as pillars of that era of superhero fiction, none of us can specifically wrap our heads around what it was about Al Pratt that made him popular enough to become a member of the original team-up of heroes.
There were dozens, probably hundreds, of generic heroes in every comic company that were simply men that wanted to fight crime (or nazis) and did so by wearing some of mask and punching people. The ones that stood out had some sort of recognizable concept that made them more interesting than the other characters. Maybe they were boxers and wore catsuits, like Wildcat. Maybe they had a hour's worth of enhanced strength, like Hourman. Maybe they dress up like a bat, create the larger concept of giving the hero an actual backstory and motivation, and revolutionized superheroes forever.
Al Pratt was short. That was his gimmick. Not superhumanly short. Just slightly shorter than most other people. Somehow, that character garnered enough of a following to become one of the founding members of the first and greatest superhero team in history; the Justice Society. He stuck around long enough to eventually gain some Nuclear themed (his name was already Atom after all) powers, but ultimately he was just a short guy that punched people.
Many of the classic DC Justice Society characters were re-imagined in the Silver Age; Green Lantern, Flash, Hawkman... the Atom was rebuilt into Ray Palmer, and suddenly made a lot more sense as a character. Still, there's a certain goofy charm to the idea of Al Pratt's tenure as a superhero, and sometimes that's exactly what you're looking for.