Gwen Stacy
In the summer of 1973, writer Gerry Conway made the decision to kill off the girlfriend of Peter Parker, Gwen Stacy, in "The Amazing Spider-Man" #121 because the editorial team felt that Gwen had become stale as a character and they wanted to instill an additional element of tragedy into Peter Parker's life. In the follow-up arcs, Conway introduced a new villain called the Jackal and let Gwen Stacy seemingly return from the dead.