There have been thousands of heroes invented since comic books first started being published. Through some oddities of copyright law, quite a few of those characters have fallen into the public domain. Anyone who wants to may use them in comic (or a movie or a tv series or a breakfast cereal).
Fantomah is, apparently, the first female comic book superhero. Her first appearance was in Jungle Comics #2 (Feb 1940). She’s one of the gloriously weird creations of Fletcher Hanks. She’s a White Jungle Goddess who, when provoked, displays godlike powers. Her body turns blue while her face becomes skull-like. And then she does horrible magical things to her enemies.