November 1939 was a big month for All-American Publications, as it debuted its second title, Flash Comics. In issue #1, Gardner Fox introduced a couple very important superheroes that would later become part of the DC Universe almost right away (even though All-American would not officially merge with DC for a half a decade).
The Flash (Jay Garrick) was the first speedster superhero, who got his powers by … inhaling hard-water gases… ¯\_(ツ)_/¯. Of course the thing to do at this point in history when you discover you have super-speed is to get a winged helmet so you can dress like Mercury! I was born in the wrong decade!