By Rick Marshall
It's no secret that Superman will be tangling with Kryptonian villain General Zod in Zack Snyder's Man of Steel reboot, but if all goes well with the film, audiences are likely to meet a few more residents of Clark Kent's rogues' gallery in future installments of the franchise. However, just because a bad guy has tussled with Superman once or twice, that doesn't mean he – or she – is ready for the big screen.
Here are 20 villains from Superman's comic-book history that we're guessing won't be leaping from page to screen any time soon.