Dr. Barton "Bart" Hamilton was Harry Osborn's psychiatrist. While treating Harry, he came up with idea of writing a thesis about the criminal mind. Being able to hypnotize Harry, he was able to learn the entire history of the Green Goblin. After finding the secret hideout of the Green Goblin, he was able to access all of the Goblin's equipment and began experimenting with them. Feeling the sense of power that came with them he felt that he was the one who should lay claim to the Green Goblin.
Since Harry had revealed Spider-Man's true identity to him, Dr. Hamilton set out to destroy Spider-Man and become the one true crime-boss of New York. He had Harry follow Spider-Man and take pictures of him destroying his clone. He then had Harry mail the pictures to J. Jonah Jameson and hypnotized him into forgetting all that he had done. He then enrages Harry during a session and they fight in the shadows. It is revealed later on that Dr. Hamilton had tied Harry up and was now the Green Goblin.
As the Green Goblin, Dr. Hamilton plotted to become crime-boss of New York. He found out that Silvermane and every crime-boss were having a meeting at a restaurant in the World Trade Center. He crashed in on their meeting and proposed that he should be the one true crime-boss. He claimed that he could offer, as leader of the underworld, something that no other leader could, which was the elimination of Spider-Man. Silvermane agreed to talk about who would be crime-boss if he could deliver on his claim of eliminating Spider-Man within twenty-four hours. He captured Spider-Man but was attacked by Silvermane's men and Spider-Man escaped. Enraged that Silvermane intervened he attacked him at Radio City Music Hall. Spider-Man shows up to stop him but could not. Silvermane was defeated and Spider-Man was knocked unconscious by one of Goblin's Sonic Toads. Goblin took Spider-Man to the same incinerator plant that Spider-Man used to destroy his clone. Goblin planned on throwing Spider-Man down one of the smokestacks, but Spider-Man woke up and was able save himself.
Spider-Man defeated the Goblin and unmasked him. As Dr. Hamilton told Spider-Man his whole plot to destroy him and become crime-boss, Harry Osborn (as the Green Goblin) attacked him. Harry and Dr. Hamilton battled and Dr. Hamilton was killed in an explosion.