#40: Green Goblin
AKA: Norman Osborn, Iron Patriot, Super-Adaptoid, Red Goblin
Powers: Super-enhanced abilities
First Appearance: The Amazing Spider-Man #14, 1964
Created By: Stan Lee, Steve Ditko
Portrayed By: Willem Dafoe, Chris Cooper
3 votes, 63 points (Top voter: Adrenaline)
Spider-Man's archenemy and deadliest foe is also his best friend's father. That's just kind of how things go for him. Norman was an accomplished businessman and scientist who had more than his share of tragedy in his life, having an abusive father and losing his wife at a young age. He was exposed to an experimental formula that enhanced his intelligence and physical traits, but also drove him mad, sending his homicidal tendencies out of control. He clashed with Spider-Man many times, and after he learned his enemy was his son's friend Peter Parker, famously threw his girlfriend Gwen Stacy off a bridge, leading to her death. He died shortly after, but returned years later, orchestrating the infamous "Clone Saga" in which Peter lost his clone brother Ben Reilly and infant daughter.
Outside of fighting with Spider-Man, Osborn was often able to use his wealth and power to gain legitimacy he shouldn't have had. He became leader of the Thunderbolts during the battle over the Superhuman Registration Act, hunting down non-registered heroes, and after orchestrating Tony Stark's fall from grace during an invasion by the shapeshifting Skrulls, became the United States Secretary of Defense. He reorganized SHIELD into HAMMER, became the Iron Man-esque Iron Patriot, created his own Avengers squad, and turned the Thunderbolts into his personal black ops unit. He went too far in launching an attack on the city of Asgardia in Oklahoma (long story), losing his authority but continuing to cause trouble, briefly becoming the Super-Adaptoid and later merging with the Carnage symbiote to become the Red Goblin. I think he is currently in one of his periods where he is "cured" of the madness caused by the Goblin formula, but it's a matter of time before he breaks bad again.
In film, Norman was played by Willem Dafoe in Sam Raimi's first Spider-Man movie, which was a pretty straightforward adaptation of the character. After a forgettable minor role by Chris Cooper in Marc Webb's The Amazing Spider-Man 2, Dafoe came back to play the character in the MCU in Spider-Man: No Way Home, ruining Peter's plan to save all the villains he accidentally brought into his universe. Dafoe is one of the best character actors alive, and his Goblin is charming, creepy, or horrifying as required in a given scene. I like Norman as a villain because he's really just an evil bastard, and his complicated personal relationship with Peter and his friends makes all of their encounters even more harrowing. The "Dark Reign" era when he was in charge of things and superheroes everywhere were always looking over their shoulder is one I look back on fondly.