MASTER COMICS (vol. 1) #1 (March, 1940). Cover by Harry Fiske.
The original and first appearance of Master Man, the "world's greatest hero!" Obviously the folks producing this comic were not aware of Captain Marvel over in their sister book, Whiz Comics.
A sick and weakly child, Master Man (we never learn his real name) met a wise old doctor who told him to "get plenty of sleep, good food and exercise." Then the doc slipped the kid the Vitacap, a "magic capsule full of vitamins, containing every source of energy known to man!"
The Vitacap bestowed onto the weakling super-strength, limited invulnerability, and super-speed. He then built a castle on top of a mountain where he could keep an eye out for trouble or situations where his powers could be put to good use.
DC Comics had just successfully sued Fox Publications for copyright infringement because the Fox character, Wonder Man, was too similar to Superman. DC then threatened Fawcett Comics with an identical suit over Master Man. Fawcett quickly acted to avoid a legal battle, and Master Man disappeared after six appearances.
However, Fawcett put up much more of a fight when DC tried the same thing with Captain Marvel, but that's another whole 'other tale in itself.
