The Birth: During the period when Harry Osborn was recovering from his drug addiction, he witnessed the final battle between the Green Goblin and Spider-Man. But it was after Spidey had apparently killed the Green Goblin that Harry realized it was his own father behind the mask of the Goblin. The shock started to drive Harry insane. He hid the Green Goblin's outfit to keep his father's secret. As Peter was trying to cope with Gwen Stacy's death, he refused Harry's plea for help. After Harry found the Spider suit in Peter's room he donned the guise of the Green Goblin and continued his father's legacy. This happened in Amazing Spider-Man #136.

The Alter Ego: Harold Osborn was the only son of industrialist Norman Osborn II. When his father secretly became the Green Goblin, he found less time for his son. Harry became frustrated and started to vent out his worrries by taking LSD.
During this time he found out that the Green Goblin was his father, but it was too late, since the villain was slain in battle with Spider-Man. Like his father, Harry's weak mind was often subjected to bouts of amnesia during which he remembered nothing of his dual identity as the Green Goblin.
Harry Osborn went on in life to marry his sweetheart Liz and soon bore a son whom he named after his father, Norman.

The Legend: When Harry found the Spidey suit in Peter Parker's room he put two and two together and learned Peter's identity. He then assumed the identity of the Green Goblin and went after the man who killed his father. Having no special strength like his father, he was easily defeated by Peter who then handed him over to the authorities. The cops were not ready to belive that Peter Parker was actually the Spider-Man or that Harry was the Green Goblin. Instead they handed Harry Osborn over to a psychiatrist, Dr. Bart 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.
He has fought the original Hobgoblin when the latter offered him proof that Norman Osborn was his father. He also battled the second Hobgoblin during the Inferno Crisis.
Towards the end of his life, Harry began imagining his father's spirit was taunting him and goading him into revenge. Eventually, Harry took an enhanced version of the Green Goblin formula and taunted Peter and Peter's wife, Mary Jane, with his knowledge of Peter's secret identity. Hungering for vengence he blew up the Osborn Foundation with himself and Spider-Man inside. But he was shocked back into the sane world when he saw his son, Normie and Parker's wife, Mary Jane. Realizing his mistake, he got everyone to safety outside before collapsing. Harry Osborn died soon afterward from side-effects of the new Goblin formula.
His costume and equipment is the same that his father had designed and used. Like his predessor, he moves around on a bat glider capable of supporting about 400 pounds and can go upto speeds of 90 miles an hour. His green gloves are specially designed to conduct electric pulses of upto 10,000 volts. The rest of his arsenal includes various gas, smoke andconcussive bombs and incendiary devices.

Amazing Spider-Man #136