Lex Luthor - Superman Vol. 1 #164
In Superman #164 (Vol. 1) Lex Luthor challenges Superman to a fist fight on a planet with a red sun. The men are pretty evenly matched and they both take quite a beating but, eventually, Superman does knock Luthor out. When Superman wins, the entire population revolts against him because Luthor has helped them to the point of becoming a hero.
Luthor only antagonizes Superman because he sees the alien as an overpowered threat. This story brings up the question of what the world would be like, and how well Lex Luthor would be received, if Superman didn't exist.
The idea that Lex Luthor might actually be the hero comes up again and again in comics. In Lex Luthor: Man of Steel (collected in hardcover verson as Luthor), Lex Luthor is revealed to be a heroic character that only antagonizes Superman in an attempt to save the world from an overpowered, untrustworthy, alien.
Further, Superman: Red Son shows Lex Luthor opposite a communist Superman in a story that begs the question: "What would happen if Superman's pod had landed in the Soviet Union?" After becoming President of the United States, Luthor is able to show Superman the error of his ways by ending the alien's reign of terror. Superman, defeated and embarrassed, goes into hiding while Luther, rather than gloating his defeat, uses his brilliance to cure the world's diseases and solve its problems.
What these three stories have in common is that they all show Lex Luthor as a champion of men, standing up against an alien threat, trying to protect human kind. In every one of these stories Lex is successful in disheartening and embarrassing Superman- forcing everyone, even the Kryptonian himself, to question his role in the world.