The Rhino. Not the brightest villain Spider-man has, but possibly the strongest. Even though I wasn't a huge fan of his in the comics, I loved him in the animated show. I can still remember the episode where Aleksei stole all the gold in New York and made a huge statue of himself. I still don't understand why he would do this, but hell, who's going to argue with a guy who can smash head first through a bus.