Norman Osborn framed his business partner, Mendel Stromm, in order to gain complete control over the business. Norman begin experimenting on a formula which resulted in transforming an Osborn employee into the Proto-Goblin. When Proto-Goblin tried getting revenge against Norman, George and Arthur Stacy manage to save his life. During the struggle, Stromm's desk was smashed which revealed the rest of Stromm's research.
Norman continued working on the formula. When mixing the ingredients, it began to turn green and exploded in Norman's face. He spent weeks in the hospital. When he was released, he realized that he was stronger and smarter than before. Thus the Green Goblin was born.
Others have sought out the formula. Jason Macendale attempted to gain the formula for himself. It was Roderick Kingsley, the original Hobgoblin that experimented on it more and perfected the formula. However, Kingsley was smart enough to not test it out on himself, and used a thug by the name of Lefty Donovan. He monitored Donovan's vitals during a battle with Spider-Man, and when Kingsley felt he passed his test, he had Donovan killed by causing his goblin glider to crash into the side of a building. Kingsley soon thereafter administered his improved formula upon himself, and is the only goblin to date who didn't succumb to insanity after being exposed to the formula.