2. Lex Luthor
Lex Luthor is up there for me as one of the greatest comic book villains ever created (troubled only by Magneto and, of course, The Joker). Essentially, wherever Superman goes, Luthor follows, fuelled by his own vanity and envy and obsessed with taking his demi-God nemesis down. Why? Its jealousy to put it simply. Although Luthor would have you believe that Superman is a menace and needs to be stopped before he accidentally destroys the world, what it boils down to is that, if it werent for Superman, Luthor would sit at the pinnacle of humanity as the most brilliant man of all time. As it stands, Superman sits above him (well, in his mind anyway, in truth, many do). Now maybe Luthor wouldnt give the Justice League too much trouble in terms of sheer power factor, but hes a manipulator and can often be seen striking deals or swearing shaky allegiances with powerful beings, all in pursuit of defeating Superman and the League a perfect way to have him factor into the threat against the league. For my money, any film that includes Superman should have at least one eye on Lex Luthor at all times, even if its main focus is on the Justice League.