Even before Dark Reign, the Green Goblin had been terrorizing the lives of Spider-Man and many Marvel superheroes. Though he originally died after slaying Gwen Stacy in one of the most infamous Spidey stories of all time, Osborn returned in the late '90s and was revealed to be an instigator in many dark moments of Peter Parker's life, including the "death" of Aunt May. Osborn's corruption has even reached his son, Harry, who is one of Parker's best friends.
Though Osborn was once merely a great foe in his Green Goblin guise, he's evolved beyond that. With the end of Secret Invasion, Norman has seized control of many United States resources, including what's left of Tony Stark's SHIELD and Avengers teams. And unlike many of his wicked peers, Osborn has done this without the use of his Green Goblin persona. What's fascinating about this turn of events, and what has drastically added to the appeal of this character, is that Osborn's power depends on his ability to keep his sanity together, something that appears more and more unlikely as time goes on. By giving in and letting the Goblin take over, Osborn might fail in retaining the power he has craved for so long.
One thing is for sure - Osborn's star is on the rise. By the time Dark Reign is finished evolving, we might be ready to reconsider where this foe deserves to be placed on our list.