Background
Harry Osborn was the college roommate of Peter Parker. He worshipped his domineering father, and tried to live up to what he thought his father's exceptions were. The pressure got to him, however, and he began taking drugs. It was a long, slow road to recovery, replete with backslides. It was during such a period that Harry witnessed the battle between his father, the original Green Goblin, and Spider-Man, that resulted in his father's death. The shock started to drive Harry towards insanity.
After discovering Spider-Man's costume in Peter Parker's room, Harry assumed the identity of the Green Goblin and tried to do in his roommate. Peter defeated Harry. The arriving authorities refused to believe either that Peter was Spider- Man, or that Harry himself was the Green Goblin. They handed Harry over to a psychiatrist, Dr. Barton Hamilton, who successfully treated Harry's insanity but who also learned everything Harry knew about the Green Goblin. Dr. Hamilton eventually went on to become the third Green Goblin -- but that's another story.
Just like his father, Harry suffered from a sort of selective amnesia and often didn't remember either his father's other life or Spider-Man's secret identity. This amnesia began to erode when the original Hobgoblin offered him proof that Norman Osborn was his father. Harry tried to use some of his father's weapons on the original Hobgoblin, with dismal results.
Harry stayed away from super-powered types for a while. During the Inferno crisis, he became the Green Goblin again and battled the second Hobgoblin. He thought about becoming a super-hero, but was forcefully dissuaded by Spider-Man.
Harry began to imagine his father's spirit, goading him to revenge. He obtained and used a modified version of the original Green Goblin's strength formula . He taunted Peter and Peter's wife, Mary Jane, with his knowledge of Peter's secret identity. He openly jetted about in his Goblin attire, even publicly confronting J. Jonah Jameson. His determination to extract vengeance caused him to try and blow up the Osborn Foundation with himself and Spider-Man inside. However, the presence of Mary Jane and his son, Norman, shocked him into a semblance of sanity. He got everyone out safely before collapsing. He died shortly thereafter, apparently from an unexpected side-effect of the Green Goblin formula.
The Movie
By now we all know that Harry finds his dad's Goblin Gear at the end of Spider-Man 2. Will he take up his father's mantle as The Green Goblin or will he hire someone else to be The Hobgoblin? So many possibilites...
James Franco: Ready to go green.
