5. Mirror Spock
There are lots of good reasons to fear the "mirror universe" version of Spock introduced in the classic 1967 episode "Mirror, Mirror." For starters, Mirror Spock is an officer of the fascistic Terran Empire – a terrifying alternate-dimensional regime in which he serves as the right hand of a violent, craven Mirror Kirk. He's nothing like the peaceful Vulcan of integrity we know and love in the primary Star Trek universe. But let's be honest: The real reason Mirror Spock placed so high on this list is his beard. That neat little goatee just screams "evil genius."