Aliens provide a different level of horror that clearly separates it from others in the horror genre. While ghosts are a supernatural and magical force of horror, there is always a sense of disbelief that accompanies them. Further, slasher movies are horrifying because of humanity's own inner demons.

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Aliens, on the other hand, are an otherworldly fear. Aliens are a distinct possibility and their motives will remain unknown until the day that humans make contact. Their murky goals and objectives, coupled with stories of Frankensteinian scientific experiments makes aliens a terrifying story subject. This article will list ten of the scariest sci-fi aliens across cinematic history.

General Zod

general zod

General Zod is, arguably, the best villain to appear in the DCEU so far. He is one of the few villains to have actually been human, as opposed to a grey CGI monster, and also had a fairly understandable plan. Essentially, General Zod wished to take control of Earth and create a new Krypton.

What makes General Zod so terrifying is that he is, basically, a dictator version of Superman. He possesses the same powers as the Man of Steel, but instead of using the powers for peace and justice, Zod uses them to gain power and make himself the ruler of all.

Martians From The War Of The Worlds

Ray looking at his hand while in a basement

The War of the Worlds is one of the most influential science fiction novels of all time. The book has never been out of print and has gone on to spawn several adaptions. From the radio play by Orson Wells, to the recent BBC and cinematic adaptions of the novel, The War of the Worlds has truly inspired and terrified generations of people.

The Martians from The War of the Worlds are typically seen as an allegory for the British imperialism that was prevalent at the time. Showcasing the devastation and fear of the inhabitants of certain countries.

Daleks

Dalek in Doctor Who Resolution

This one may be considered controversial, but the Daleks did make a cinematic appearance in 1965's Doctor Who and the Daleks. The Daleks are an iconic staple of science fiction horror. Their debut in the 1960s caused many children to hide behind the sofas and helped cement Doctor Who as not only a show that will terrify viewers at times, but also as a cultural phenomenon both in the UK and across the world.

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While the design of the Dalek is seen to be absurd by modern audiences, no one can deny just how terrifying this creature would be to deal with. The Dalek is full of hate and bent on universal domination, it truly is a terrifying foe.

IT

What could be scarier than a creature that turns into your greatest fear? A creature that turns into your greatest fear while also spending most of its time as a homicidal clown. The creature is an intergalactic being that crashed to Earth thousands of years in the past and awakes every 27 years to feast. It is clearly alien in nature and its ability to shapeshift into whatever scares us is, by definition, terrifying.

The two movie versions of IT, both the recent adaptation and the 1990s miniseries, skirted away from the cosmic horror elements of IT.

The Thing

John Carpenter - The Thing

Some may consider the Thing and IT to be incredibly similar. Both characters are intergalactic creatures that are able to shapeshift. However, where the two are different is in their success rate.While IT is undoubtedly terrifying, the outer space clown is defeated by several children. On the other hand, the Thing is able to successfully defeat and trick several fully grown humans in an isolated research base.

Additionally, the body horror in The Thing separates it from IT in a manner that makes it far more disturbing to think about long after the movie has finished.

Aliens in The Fourth Kind

The Fourth Kind is one of the most underrated horror movies in recent years. While the notion of alien abduction is always a scary concept, this movie does a marvelous job of increasing the fear factor. One of the most effective elements of the movie is the distinct lack of aliens in it. This leaves the aliens largely to the imagination of the viewer. This lack of clarity on the aliens themselves, coupled with the clear fear and trauma of the victims makes for a disturbing watch.

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It goes without saying that you will not go to bed easy after watching The Fourth Kind. 

Darth Maul

Darth Maul in Star Wars Phantom Menace

What is interesting about Darth Maul's addition to this list is that the Sith manages to skirt along the boundary between cool and terrifying. Maul's double-ended lightsaber and unique fighting style make the character look incredibly cool and unique in the Star Wars universe.

On the other hand, the evil intentions, appearance, and abilities of Maul make him terrifying. The demon from Insidious resembles him, and it goes without saying that you wouldn't want to run into Maul in a dark alley.

Xenomorph

The Xenomorph drools in Alien Covenant

Perhaps the most iconic horror alien of all time. The Xenomorph is a terrifying creature that has captured audiences' imagination for decades. In addition to being incredibly powerful, fast, and aggressive, the creature also possesses acid-like blood and above-average intelligence. If this is not enough, the exoskeleton of the creature is strong enough to resist powerful attacks, such as gunfire.

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While the Xenomorph is terrifying enough as an adult, it is even scarier when young. The young Xenomorph buries itself deep into a host, acting as a parasite before then bursting out the body. This is a truly horrifying creature.

The Predator

Predator Close Up Face

The Predator is a highly advanced and highly intelligent alien species. The Predator species has a culture that is based heavily around hunting and stalking prey. Predators see hunting as a sport and, consequently, do so for the challenge rather than for any form of sustenance.

What is so scary about the Predator is the fact that its intelligence is so great that once it wants you dead, there is a good chance you will be. Additionally, there is also an element of dehumanization in the hunt of the predator that is always scary. The Predator sees you as an object, whether it be a challenge or just some fun, this alien does not see you as anything more than sport.

Thanos

Thanos

The Mad Titan certainly deserves a place on this list. While he may not be considered terrifying in the same sense as others on this list, Thanos is certainly an intimidating character. Thanos managed to defeat several members of the Avengers, including the Hulk, on his quest to collect all of the infinity stones and wipe out half of all life in the universe.

Thanos is also one of the most successful aliens on this list. He achieved his goal and was able to defeat the Avengers to do so. He didn't have to resort to trickery or deception, he was simply too powerful for Earth's mightiest heroes and this was truly terrifying.

NEXT: 10 Most Terrifying Aliens In Sci-Fi TV History