Harold "Harry" Osborn is a prominent supporting character in Marvel's Spider-Man series. He is Norman Osborn's son who is terminally ill, unbeknownst to his best friends Peter Parker and Mary Jane Watson, until they found out his actual situation in the near end of the first game.
Harry is the only son of Norman and Emily Osborn. His childhood was happy, although he suffered the loss of his mother at the age of 15, due to complications from Oshtoran Syndrome.
Harry was a childhood friend of Peter Parker and Mary Jane Watson, which lasted into their adulthood. He graduated at the top of his class from Empire State University. At some point after this, he started an internship at Oscorp, hoping to eventually follow in his mother's footsteps as an environmental attorney.
However, he had inherited his mother's Oshtoran Syndrome and began to experience complications. Unwilling to put his friends through the hardship he felt during his mother's illness, Harry kept his condition a secret, pretending to be busy or hungover from partying when his sickness got in the way.
Eventually, Harry's condition became critical. His father had him directed to take an experimental medical treatment, which would take years for him to complete. Harry agreed to do so and enter into stasis chamber to buy enough time for the treatment to be complete, leaving a note in his diary for Peter and Mary Jane should the treatment go wrong. Norman explained Harry's resulting absence to the world as Harry being in Europe managing Oscorp's international operations. Because of how close the three of them were, Peter and Mary Jane texted and left numerous phone calls to Harry to check in on him, none of which were ever responded due to Harry's stasis.
Before beginning the treatment, Harry left recordings for Peter at some of Oscorp's various research stations, which were set up by him to monitor air pollution in New York, a dream he carried out for his late mother. In these recordings, he asks Peter to finish what he couldn't. Following Norman's shutdown of Octavius Industries, Peter began visiting the associated research stations to help his friend.
While breaking into Norman's apartment as part of a covert investigation, Mary Jane discovered the truth about Harry's condition, which she shared with Peter. She also found journals he left behind which indicated that he knows his father loves him and is trying to help "in his own way", but was highly aware of just who his father is and how he operated. The journals also left instructions that Peter and Mary Jane be told about his condition after he went for treatment.
While it is unclear what the immediate results were of Harry's treatment, he could be seen at the conclusion of the game inside Norman's hidden lab, where he was kept in a holding tank in a clear green liquid with a black web-like substance clinging to him until a cure could be found for his condition. As Norman placed his hand on the tank when he came to visit him, the substance reacted and copied him, which Norman fails to notice.
After a year or so, Harry regained consciousness and woke up to a news broadcast reporting Roxxon's criminal activity and Rio Morales's successful election as councilwoman. His father saw this and told the doctor looking over his son, Curt Connors, to get him out of stasis immediately, despite the warning of his ongoing illness.
Harry seems to be a good-natured and intelligent man, hoping to follow in his mother's footsteps as an environmental attorney. Harry's recordings in his laboratories indicate that he is a kind individual with a strong sense of social conscience, sincere in his desire to continue his mother's legacy by cleaning up New York and making it a better place for his fellow man. He seems to have traits of the "lonely rich kid" trope, as Mary Jane recalls that in their childhood, Harry was noticeably more content watching cartoons in Aunt May's apartment than in his family's penthouse on an advanced TV.
Harry Osborn's first appearance was in Amazing Spider-Man #31 (December 1965).