In Amazing Spider-Man #39, the Green Goblin did the unthinkable: he discovered Spider-Man’s secret identity. He didn’t do this through clever deduction or during a battle—he simply just followed him home one day. It was brilliant in its own simplicity, but it worked easily after the Goblin deadened Parker’s spider-sense with a specialized gas.

This is the highpoint of Stan Lee and John Romita’s time on the character. In Amazing Spider-Man #40, Spidey one-upped the Goblin by finding out that he was actually Norman Osborn. Together, the two issues effectively changed the characters' entire relationship. Ever since then, their battles have been much more personal, with loved ones and dear friends winding up as casualties.

Unmasked marked the birth of Goblin's sadistic side; at the time, it was revolutionary for comics to have a hero and villain know each other’s identities and be so intimately attached to one another. The story's events shaped the web-slinger's entire career, changing his relationships with Gwen Stacy, Mary Jane, Harry Osborn, and almost everyone else in his life.