A comment by a graduate student in the sequential art class I teach at Pratt, lead me to an idea that came from Marc DiPaolo in his book War, Politics and Superheroes: Ethics and Propaganda in Comics and Film. He quotes William Shakespeare (from Twelfth Night) as saying "some men are born great, some achieve greatness and some have greatness thrust upon them." He goes on to apply this, respectively, to the characters of Superman, Batman and Spider-Man.
This is, of course, an extremely astute comparison that places these characters on a great archetypal spectrum of heroism and points up what powerful and compelling icons superheroes can be. Ultimately, though, it seems to highlight just how far ahead of everything William Shakespeare actually was.