The Green Goblin

There would be other goblins, such as the Hobgoblin, and other Green Goblins, but no other goblin has the menace or staying power of Norman Osborn, the Green Goblin.

He knows Spider-Man is Peter Parker. He murdered Peter Parker's girl-friend, Gwen (Amazing Spider-Man # 121, June 1973). Spider-Man then battled the Goblin to the death and the Green Goblin died, impaled through the chest by his own glider (Amazing Spider-Man #122).

Norman Osborn's son, Harry, then becomes the Green Goblin (Amazing Spider-Man #136).

Later, Bart Hamilton becomes the Green Goblin (Amazing Spider-Man #176).

Norman  Osborn recovers from death and returns (Amazing Spider-Man #418).

Phew.