Origin

Harry Osborn enrolled in Empire State University with his friend Gwen Stacy. They rapidly became friends with Flash Thompson. Flash was a star football player and tried to introduce Peter Parker to Gwen and Harry. Peter was worried about his Aunt May being poisoned by his radioactive blood at the time and so didn’t respond to Flash's attempt at introductions very well. Gwen, Harry and Flash didn’t appreciate Peter's seemingly "snobbish" attitude towards them at the time.

As a consequence of Peter's apparent snobbish attitude, Flash and Harry tried to annoy Peter. Little by little though, Peter reconciled with Harry and they became friends. That is why when Green Goblin, Harry’s father, paid for a huge apartment for two, Harry asked Peter to be his housemate and Peter accepted.

Everything in Harry's life seemed great. He had good friends, and a gorgeous girlfriend (Mary Jane). But then MJ dumped him and his father started putting intemse pressure on him by laying all of his hopes on Harry. As a consequence of all this, Harry fell on drugs. Harry went to Detox which healed him physically but left him still psychologically weak.

After the death of the Green Goblin (Norman Osborn) during a battle against Spider-Man and the discovery of the real identity of Spider-Man, Harry Osborn became totally mad. He decided to follow in the footsteps of his father and become the new Green Goblin. He was defeated by Spider-Man and Harry ended up in a psychiatric hospital.

Like Father, like son...

With the help of Simon Cowell, Harry would regain his previous life. He met Liz Allen and she became his girlfriend. Harry proposed to her and Liz accepted. Harry and Liz had a child together, Norman Osborn Jr.

When Hobgoblin tried to obtain theGreen Goblin formula from Harry, Harry decided to again wear the costume of Green Goblin in order to protect his family. But Harry fell into madness and began to attack Spider-Man. During a battle, Harry launched a bomb inside the Osborn Foundation where Norman Osborn Jr and Spider-Man were. Realizing what he had done, Harry regained his sanity and saved everyone. Harry collapsed dead, poisoned by the Green Goblin formula.

With the Spider-Man: Brand New Day storyline/reboot, Harry Osborn is alive and well and, as of yet, has not returned to being Green Goblin.
He is dating Lily Hollister, and is best friends with Peter Parker.

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Movie

Harry in the movie's is played by James Franco. In Spiderman 1, Harry is introduced as a new student at Peter's high school who flunked out of every private school his father put him in. Harry showed up at one of his school's field trips to a spider museum and introduced Peter to his father Norman Osborn. Norman was impressed with Peter's intelligence. Peter and Harry then enterd the museum to examine the spiders. When Harry saw that MJ was by herself he urged Peter to go talk to her, Peter said no and insisted that Harry go talk to her so Harry did. Harry talked to MJ and actually used one of the facts about spiders that Peter had told him earlier to start up a conversation with her. Then at the museum Peter started getting picked on as usual, Harry stepped in to help Peter and nearly got into a fight with Flash until the teacher broke it up.

Harry and Peter finally graduated from high school. At the graduation he saw MJ and Flash argue then break up and so harry took advantage of the situation and hooked up with MJ.

Later in the movie Harry was finally going to introduce MJ to his father for the first time at Thanksgiving dinner. Harry introduced MJ and his dad was impressed. Dinner didn't go as well as Harry had planned and Harry's father stormed out after discovering Peter was Spiderman. Harry followed his father out to talk to him. Harry and Norman argued about MJ and Norman said some hurtfull things that MJ overheard. Harry didn't stand up for her as much as MJ would have like him to so MJ then stormed out after arguing with harry, their relationship pretty much ended at that point.

At the end of the movie Harry watched as Spiderman laid his fathers dead body down in the living room of his home. Harry then pulled out a gun and attempted to shoot Spiderman, but Spiderman was gone by the time Harry looked up. At his fathers funeral Harry swore that Spiderman would pay, thinking that Spiderman had killed his father.

Spider-Man 2

In Spiderman 2, Harry is a strict businessman for OSCORP. He worked with Dr. Otto Octavious by financing his project and therefor putting OSCORP on the map in a way his father never dreamed of. Once Otto has the project completed and ready for testing, Harry and Peter along with others watched as Otto demonstrated what his project was about. Unfortunately, when Otto activated the machine, it entered into an unstable state. Harry screamed at Otto to shut the machine down but Otto wouldn’t listen. Everyone else left before things got bad except Harry who was too busy yelling at Otto. When the machine finally started to explode, Spiderman came to the rescue and saved Harry from the explosion. Harry, although greatful, told Spiderman that what he did for him wouldn’t change the way he felt about the web-slinger.

Later, while Harry is down and depressed about Otto's project failing and therefor not helping out OSCORP the way Harry had hoped it would, Otto came to visit him on his balcony. Otto demanded that Harry give him what he wanted, Harry refused, and so Otto used his mechanical arms to lift Harry over his balcony and threatened to drop him. Harry immediately offered to come to an agreement with Otto, and Otto then brought Harry back onto the balcony. Harry told Otto that if he would bring Spiderman to him alive he would then give him whatever he needed.

Once Doctor Octavious ("Doc Oc") had his fight with Spiderman and defeated him, he brought him back to Harry. Harry then said he would get Otto what he wanted and Otto then left. Harry finally got what he wanted and was ready to stab Spiderman, but he then decided to take off Spiderman's mask to see who he was first. It was then when he discovered that it was Peter Parker who was Spiderman. Harry dropped his knife, shocked at the discovery. Peter then woke up and tried to convince Harry to leave him alone because he had to save MJ. Harry was still shocked so Spiderman just slung away out the window.