"The X-Factor comics circa mid-1990s had a great deal of fun with this one:Dick Chalker was a mutant who could turn himself into a manlike dinosaur creature. He used his powers to commit murder, robbery and postal fraud, and inspired hatred of mutantkind in the rest of the Chalker family.
Dick's cousin Rick Chalker decided to act on this hatred of mutants. In true MadScientist fashion, he successfully replaced his hands with enormous, razor-sharp propeller blades. Calling himself the Number One Fan, he was ready to kill every mutant in the world... only to discover that he couldn't open the door out of his lab with them. When he tried to slap himself in the forehead in frustration, he cut the top of his head off.
The third cousin, Professor Vic Chalker created a massive robot battlesuit to avenge Rick. In making the first version of the suit, he forgot to take his measurements so he couldn't fit in it. In making the second version, he didn't give it enough of a power supply and it ran out of juice five seconds after he started it, becoming trapped inside in the process. In making the third version, he gave it enough power but forgot to waterproof the suit. He fatally electrocuted himself after he took the suit out in a rainstorm.
Dick, now calling himself "Carnivore", decided that Rick's and Vic's deaths were on his conscience and decided to avenge them by killing every mutant on Earth so none of them could abuse their powers the way he did. Unfortunately, as he stepped out of his house to commence his killing spree, he was immediately killed by a truck.
All of this led up to an X-Factor annual issue where a mutant-hating former classmate of Strong Guy's showed up, having devoted his life to the dark arts and become a servant of Mephisto. In order to defeat X-Factor, he brought back their three greatest enemies from the dead — the three brothers who had died over the past three issues, none of whom had so much as been seen by X-Factor. So in the massive, climactic battle, an Unknown Rival resurrected three more unknown rivals. When the villains introduced themselves, Polaris asked if they were sure they had the right X-team.
Strong Guy: That figures! Only we could have a bunch of "greatest enemies" that we never heard of."
http://tvtropes.org/pmwiki/pmwiki.php/Main/UnknownRival?from=Main.SchoolgirlRival
Let's just hope North Korea never sees that page...