10. Sheldon Cooper (The Big Bang Theory)
Okay, first things first; I know Sheldon isn't a villain as such, and the Doctor is indeed someone he admires but, should Sheldon ever meet the Doctor, he would undoubtedly be incredibly intimidated by the fact that the Time Lord is so vastly more intelligent than him - and we know how Sheldon reacts to people who outsmart him. One wayward comment from the Doctor, or anything that inadvertently makes Sheldon feel less intelligent than him, and Sheldon would put the Doctor in the same position he had previously placed the likes of Brent Spiner and Wil Wheaton - at the top of his list of 'mortal enemies'. Unfortunately for Sheldon, he simply doesn't have a chance of posing a threat to the Doctor, who would simply be several steps ahead of him at any given point. Sheldon is undoubtedly a genius in real world terms, but the Doctor's genius is simply way beyond that. Everything Sheldon knows is possible and within the realms of real world physics. The Doctor... not so much - the things he knows would be too much for Sheldon's comparatively simple mind to handle and, while I'm sure he'd give Sheldon a pat on the back for trying, he'd be like an ant beneath the Doctor's metaphorical boot in a direct battle of minds.