1. Lex Luthor
Did you think anyone else was going to claim the #1 spot? Lex Luthor has been Superman's arch nemesis for decades and has evolved into more than just the mad scientist of the original comics. Now a corrupt businessman, Luthor has been given a rich backstory and psychology, being arrogant enough to think he is the hero rallying against an invading alien who will eventually turn on Earth. Though he knows he's evil, he largely believes every action he takes is for the greater good of the world. Hinted at in Man of Steel, Luthor is already established in Metropolis as a businessman given the numerous times LexCorp appears in the background. Luthor is also the link to many of the villains I have listed: it was his chemicals which turned Rudy Jones into the Parasite; he funded and performed the Metallo project; he has the means to hire a mercenary such as Deathstroke. The only one he's not immediately connected to is Brainiac, but Luthor wouldn't hesitate to step in as the hero and claim Superman's been working with Brainiac all along. Given the destruction of most of downtown Metropolis, it also gives a very good reason for his claim from the comics, "I own half of Metropolis", to Superman to be quite true. Add to the fact that Zod discarded his armour in an abandoned LexCorp construction site and everything is in the mix for the definitive version of this character to finally appear. I just hope the rumors about WB's courting of Bryan Cranston in the role prove to be true.