7. The Gorn
Some Star Trek villains are complex characters, shaded with ambiguous motivations and moral nuance. Not the Gorn. They're just angry, hissing lizard-men that will probably rip your head off if you give them the chance. In the 1967 original series episode "Arena," one representative of the species tries very hard to kill Kirk when they're forced to fight each other by a third alien race. The Gorn captain's brute strength gives him the upper hand, but Kirk eventually outsmarts him – and chooses to spare the life of the snarling reptilian that was just attempting to murder him. Generous guy, that Kirk.