Who Is Superman?

Elliot S. Maggin's Lex Luthor has multiple identities so he assumes that Superman also has, like maybe:

Morgan Edge
Joe Namath
Bruce Wayne
Pete Ross
Graig Nettles
Jim Rice
Edward Kennedy

Luthor does not try to expose any of these aliases because he assumes that Superman would just create new ones. Superman plays the Clark Kent role so well that Luthor never suspects Kent although the guy spooks him somehow. There are times when Luthor is close to the truth but unable to see it.

Although Siegel and Schuster created Superman, several subsequent writers have invested a lot more creativity and ingenuity into the character and his supporting cast.