2. Krona
Krona is a villain who has been a part of both the DC and Marvel universes, making him unique in that nature. Krona was once a scientist and when he worked as one he was completely obsessed with being able to see how the universe was formed. However, while attempting to craft a machine to allow him to do that, an accident occurred that allowed evil to come into the cosmos. He was then punished and turned into energy and now he attempts to destroy the universe whenever he gets the chance.