Who else were you expecting to see here? While he may not be Superman's most formidable foe in terms of sheer strength (though those armoured costumes of his have certainly helped in that respect), it's Lex Luthor's intelligence and irrational hatred and fear of the hero which make him dangerous. Believing that Superman poses a threat to the human race, Lex has made it his life's goal to end the Man of Steel. Manipulative and evil to his core, Lex has done anything and everything in his quest to take down Superman, even becoming the President of the United States at one point. In recent years, he's blackmailed his way into the Justice League and become a reluctant ally of Superman's, but still plots against him - creating an Amazo virus which nearly wiped out Metropolis for example - and the entire DC Universe as a whole!
