Who was the first super hero in DC comic books?

Superman was the world's first SUPERHERO (Created in 1932, sold to DC in 1938, first appearance Action Comics #1, published April 18, 1938). Superman was NOT the world's first comic book hero.

The Crimson Avenger was the first MASKED CRIMEFIGHTER (Detective Comics #20 October 1938).

Batman appeared LATER (Detective Comics #27, May 1939).