Comic book superheroes have a near-endless supply of supervillains, scoundrels, and all-around bad guys to punch in the face for the sake of good and the protection of the innocent. Sometimes these threats come from distant worlds or alternate realities, but other times evil comes from the actions taken by our most beloved heroes.
Often times, a hero's rival will actually have their villain backstory closely tied to the hero themselves, with their (usually) well-intentioned actions having "made a monster". This makes those villains all the more compelling, as their fates are very much bound with that of their nemesis, and their rivalry is all the more exciting for it.
Of course the superheroes never really set out to create their worst enemies, despite what many news publishers in their universes would say. Most of the time, heroes don't even realise until too late the monsters that they have unwittingly sent out into their worlds, and begin to unleash absolute havoc.
Both Marvel and DC have dozens of villains that have been created by superheroes. These are just a few of the most diabolical supervillains created by their rival superheroes.
Your friendly neighborhood writer across the pond in the United States' west coast with a deep love for everything nerdy. He is a big fan of Batman and Godzilla and is always excited to see what the future of the entertainment industry will bring.