While no doubt always a classic Spider-Man villain, Doctor Octopus never really had a defining story which saw him push Spider-Man to the edge. However, that all changed when the villain - who was dying after sustaining years of blows to the head - managed to switch minds with Peter Parker, leading to the hero dying in the villain's failing and broken body. As poorly told as this story was in places, seeing Otto Octavius become the "Superior" Spider-Man and wreak havoc in Spidey's life was fascinating, as was his decision to restore Peter's mind at the cost of his own. That doesn't necessarily make him a good man after all he's done, but Doc Ock is without a doubt one of Spider-Man's most complex foes.
