The Green Goblin has proven himself to be Spider-Man's greatest enemy in any number of ways over the years, whether it's killing his girlfriend, allegedly murdering his newborn child, or generally just making Peter Parker's life a living hell. He was the first villain to learn Spidey's secret identity, and while others have tried to take his place (including his son, Harry), Norman Osborn is the one true Green Goblin and a truly despicable person. Of course, the less said about the time the villain seduced Peter's girlfriend and got her pregnant, the better...it is after all one of the most universally hated stories ever!