Depends on when, but the answer is never Harry Osborn, who is/was the second Green Goblin. For a while they revealed it was Ned Leeds. Then it was supposed to be Jason Macendale (who at one time was Jack O'Lantern), and in the end it was revealed that fashion mogul Roderick Kingsley was the original Hobgoblin, who hypnotized Ned Leeds into thinking he was the Hobgoblin, and then set him up to die. This was a long and convoluted story, but that's the answer.
