Who was the first Marvel superhero?

Namor the Sub-Mariner was the first Marvel superhero and made his debut appearance in 1939. The character was created by William Blake "Bill" Everett and was first published by Timely Comics, the precursor to Marvel Comics.

Namor was first created for a giveaway comic book that was never released. The character eventually made his first appearance in the pages of "Marvel Comics #1," which was the first title published by what would later become Marvel Comics. Namor is considered to be an antihero, and he was often featured in stories where he opposed other heroes in order to serve the greater good.