Conquermind is an alien being who is responsible for The Northern Light gaining his super powers (more on him later). In The Northen Light's final adventure, Conquermind and Northern Light have a (literal) battle of the minds. In the end Northern Light's will has stronger, and Conquermind was finally defeated.

Superman's main enemy Lex Luthor, when he was still drawn by Joe Shuster. Luthor first appeared in Action Comics #23 (April 1940). In one of Luthor's first schemes (Action Comics #47) he uses a meteorite called The Powerstone to give him powers similar to Superman's. Eventually, Superman managed to wrestle the stone away from Luthor. Since then, Luthor has continued on to plight Superman, using his incredible mind.