A superhero can't be classified as such without having antagonists, enemies, villains, etc. All of the best superheroes have them. Spiderman is no different. He has managed to develop plenty of enemies over his lifetime. I guess that's what a life of fighting crime gets you. Some of Spidey's most notable enemies are Venom, Mysterio, Sandman, Chameleon, Doctor Octopus and Green Goblin. We'll take a look at each of their back stories below.
Venom: Venom (Eddie Brock) was created from an alien symbiote costume, which was a once worn by Spiderman during the Secret Wars. Eddie Brock, a reporter, somehow gets ahold of the costume. He uses it to avenge himself against Peter Parker who he believes ruined his reputation and caused him to lose his job. When Brock wears the venom costume, he is able to harnesses the same powers that Spiderman can. He is also immune to one of Spiderman's most powerful weapons, his Spider-sense. Brock would later become Anti-Venom.
Sandman: The Sandman was originally a convict named Flint Marko who escaped from prison. Caught on a vacant beach where nuclear testing was occurring, Marko became sliced with molecules of sand, at the cellular level. He would transform into a giant mass of sand and developed several, different personalities.
Green Lantern: Green Lantern is one of Spiderman's most well-known and dangerous antagonists. Originally, Norman Osborn, a scientist and business professional, Osborn would become the Green Lantern when while working with an experimental formula, it exploded on him. As a result of this explosion, Osborn developed super powers. When his hopes of becoming New York City's top crime boss, are dashed by Spiderman, the Green Lantern vows to ruin him.
Green Lantern was the first major villain to learn that Spiderman was actually Peter Parker. He was also involved in the death of Parker's first serious girlfriend, Gwen Stacy and the kidnapping and disappearance of his and Mary Jane's baby. Lantern was also behind the Clone Saga.