Many people believe that extraterrestrial life is out there. If it is anything like we see on TV, contacting those extraterrestrials might not be a wise idea. Dozens of TV shows have introduced individual aliens and alien races who have a single-minded agenda of conquering Earth and exterminating or enslaving humanity. These five alien races stand out as some of Earth's most terrifying alien enemies:
Daleks (“Doctor Who”):
The Doctor tangles with some nasty aliens in his travels through time and space. None of them are quite as consistently bent on wholesale destruction the way the Daleks are. This is a species so convinced of its superiority that it wants nothing more than to wipe out everything else that is not a Dalek. Nothing can turn them or impede them from this quest. The only good Dalek is essentially a dead Dalek.
The Borg (“Star Trek: The Next Generation”):
It's true that the Federation has dealt with a host of bad guys from Klingons to Romulans. Still, none of them inspire the level of fear that the Borg do. When you lose to the Borg, you lose everything. Your individuality, your personality and your humanity are gone. You become overrun by cybernetic implants and are connected to a hive mind dominated by a single Borg queen. It has to make life boring on a Borg cube. What is the point of conversation when no matter who you speak to, you are essentially talking to yourself?
The Visitors (“V”):
Any time you meet an alien race want to promote world peace and help humanity better themselves, run to your nearest militia group and raid their cache of illegal weapons. "V" and its various sequels taught us these humanoid aliens are actually disguised reptilian beings waiting to serve us up for lunch. And they will swallow rats and other small mammals whole to drive the point home!
Goa'uld (“Stargate SG:1”):
Many people have a fear of snakes and that fear is perfectly reasonable. Some snakes can release poisonous venom when they bite their victims. The Goa'uld – a race of alien snakes – did much worse than release venom. They plunged through the back of their victim's necks and wrapped themselves around their brain stem. The person became a prisoner in their own body as the Goa'uld changed their voice, controlled their mind and used them to kill and enslave people across the galaxy. Rattlesnakes seem rather harmless by comparison.
It's not bad enough to create robots who want to destroy all humans. The problem with Cylons is that they look exactly like humans too. It's hard to fight an enemy when you can't tell them apart from your own kind. Cylons wage war on the human population of the 12 colonies and massacre them in a well-executed sneak attack that leaves a scattered band of survivors. It goes to show robots can do everything more efficiently than humans – including genocide.