The Birth: It all started in Amazing Spider-Man #14. A new and one of the soon to be most imitated criminals arrived on the scene with a view of becoming the greatest crime-lord of the world. Though the Green Goblin was intorduced in Amazing Spider-Man #14, his origin was revealed only in ASM #39.
..... Soon after Norman Osborn II got his partner; Mendel Stromm imprisoned for embezzlement (similar to Vulchy, eh!), he tried Stromm's experimental formula. Though seemingly at first it was an accident, in keeping with true comic book style, Norman Osborn realized while recovering in hospital that the mishap had augmented his intelligence and strength to superhuman levels. Downside - the change slowly drove him insane. Osborn donned a green suit, dubbed himself the Green Goblin and pluged himself into a life of crime.

The Alter Ego: Norman Osborn II was a ruthless industrialist who cared more for greenback with dead presidents. But he did find time for his family and was a real pal to his son, Harry. But that was before the accident altered his psyche.
There was a brief period of time when Osborn was cured of his lunatic behaviour as a result of amnesia. While recovering in hospital he told Harry that though the past was lost to him, the future still lay ahead and it would definately be a good one.
Unfortunately, the change was temporary. Quite some time after this, when Harry was going through LSD withdrawal symptoms, his father blamed his friends for his drug addiction. In addition to his son's problems Norman Osborn was informed of his financial ruin, which eventually pushed him over the edge.

The Legend: When the Green Goblin first appeared on the scene, his plan was to establish himself as the boss of the underworld. To establish his reputation and become a force to be reckoned with, he decided to get Spider-Man's scalp under his belt.
His elaborate ploy involving the Enforcers and Spidey together starring in a movie, blew up in his face when they stumbled upon Hulk's secret hiding place. Gobby escaped and tried to get his revenge on Spidey on several occasions, but each time he was humiliated with his own defeat.
Later on, when Green Goblin realized that his heads-on approach wasn't accomplishing much, he rigged a robbery scene to lure the web-slinger. Naturally, Spidey arrived, saved the day and then went about his normal business as Peter Parker; unaware that he was shadowed by the Green Goblin who watched his transformation into Peter Parker. With his identity now unmasked, Gobby confronted Parker outside Aunt May's house. Gobby took Parker to his lair where he revealed to him his own identity to the wall crawler. Peter was able to free himself from the Green Goblin's bonds and in the fight that ensued, Gobby fell backwards, knocking live wires into volatile chemicals and he took the full blast of the electro chemical shock. Though he didn't die that day, his memory was wiped clean of the years that he spent as the Green Goblin.
But his alter ego could not be suppressed. Due to his son's drug addiction and the added depression of his own financial ruin, he went crazy and his split personna soon emerged as he recollected everything. Knowing Spidey's identity, the Green Goblin decided to strike at Peter Parker's friends. He kidnapped Gwen Stacy and threw her off the Brookyln Bridge. Though Spider-Man webbed Stacy's feet, the stop was too sudden and she died.
Fueled with revenge, he charged against the Green Goblin and trashed it out with him. The Goblin commanded his bat glider to ram Spider-Man from behind. But with his trusty spider-sense he was warned of the danger and jumped out of the way in the nick of time. The glider might have missed Spider-Man but it hit the Green Goblin in the chest, apparently killing him.
When Harry Osborn found that his dad was dead, he removed the costume and his identity remained a secret.
..... For years, Spider-Man believed that ol' Greenie had died in the warehouse, but the truth was that, though Marvel created many lookalikes, they just had to bring the original guy back into the picture. So, as the story goes, it seemed somehow Norman Osborn II survived the blow to his chest because of his healing ability and then fled to Europe where he started from scratch accumulating vasts proportions of wealth and creating his business empire again. He also became a very powerful crime-lord.
After stabilizing himself he returned to NYC and took over the Daily Bugle. Since then he has terrorized the lives of everyone close to Peter Parker.
He was responsible for the entire clone saga. Norman Osborn II funded the experiments of Miles Warren to create the Peter Parker clone. Warren created several clones including Ben Reilly, Kaine and Spidercide. Norman then recruited the Scriers, Gaunt (who was previously Mendel Stromm)and Seward Trainer to help him turn Peter's life upside down. The Goblin's plot made Peter Parker think he was actually a clone while Ben Reilly was the real deal. He also stole Peter's baby and made him think that MJ had given birth to a stillborn. When Norman's clonage plot was uncovered he tried to kill Peter. But instead, Scarlet Spider got in the way and was killed.
Most of the Green Goblin's ensemble has been designed by himself. 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 #14	Amazing Spider-Man #121	Amazing Spider-Man #122