10. The Thing from The Thing

John Carpenter's The Thing is regarded as one of the best science fiction remakes of all-time (despite what our editor in chief has to say about it), and it's not because of Kurt Russell's rugged beard. No, what truly elevates The Thing above typical science fiction thrillers is the film's aliens, which lurk within the bodies of its characters and burst out in the film's most surprising moments. Few can forget when Norris' head suddenly separates from his body and crawls around the room on its own grown appendages. Not only does this fit the film with truly frightening special effects, but Carpenter creates a situation in which both the characters and the audience are not sure what will happen next. No one is trustworthy when there may be an alien life form living inside them. The Thing remains one of the truly scary thrillers of science fiction, and the creatures, demonstrating state-of-the-art effects that still impress and frighten moviegoers almost three decades later, remain a factor in the film's most memorable moments.

9. The Predator from the Predator and Alien vs. Predator franchises

Definitely one of the meanest aliens on our list, the Predator supercedes humankind in both biological and technological sophistication. Top this off with a sideways mouth, huge teeth, dreadlock-like hair, and an invisible cloak, and you have one intimidating alien. Simply put, the Predator is a ruthless killing machine and one of the few who will actually laugh at you when he's ready to self-detonate. There's not much more to say about this guy other than to watch out if you see him ... especially if he brought his friends along.

8. Superman from the Superman franchise

Look! Up in the sky! It's a bird! It's a plane! It's ... SUPERMAN!

Superman is not only one of the best aliens ever, but he is the most iconic superhero of all time and, with all of the most basic superpowers the comic book world could dream of -- super strength, super speed, flight, X-ray vision, and heat vision -- along with good morals, represents exactly what it means to be a hero. Though not exactly dynamic, Superman is the paradigm of heroism, devoting his life to that ever-mythic triad: truth, justice, and the American way.

7. Nibbler from the Futurama franchise

A millenial-aged being and a "celebrated pooper," Nibbler is the pet of Captain Leela in the Futurama series. While he is adorable and can poop dark matter to power a spaceship's engines, Nibbler and his people are actually a super-intelligent race that seeks to protect the universe. Boasting fearsome spaceships like the Kitten class cruisers and speaking with the wisdom of the eons, Nibbler and his people are the unsung (and often ignored) heroes of the universe. To Leela he is an adorable little pet; however, without Nibbler the entire universe would have been destroyed by giant brains!

6. King Ghidorah from the Godzilla and Mothra franchises

It's easy to label King Ghidorah simply "giant monster," but his (albeit murky) origins in the Godzilla films indeed place him as an alien. Ghidorah first arrived on Earth in a big rock, and has been wreaking havoc ever since. This three-headed dragon is not only ... a dragon with three heads (and two tails), but he also breathes lightning out of each of them, is super-fast, and can create hurricanes with his wings! Not a good combination for his enemies. All in all, this is one of the butt-kickingest aliens you'll ever see.

5. The Queen Alien from the Alien franchise

Never bother an angry mom -- especially if she's a massive killing machine from another planet. While the queen alien's function, of course, is to produce more aliens, she can be one mean creature when she needs to. This alien makes the list because of her sheer ferocity and power, exemplified in a showdown with Ripley at the end of Aliens. Stand back. This is a catfight you don't want to get in the middle of.

4. Klaatu from The Day the Earth Stood Still (1951)

The second of two one-hundred-percent-human-looking aliens on our list, Klaatu comes to Earth with a stern warning to our nations: stop your fighting or my race will stop it for you. The best thing about this character (thanks to the actor who plays him, Michael Rennie) is the authority he commands despite a completely understated demeanor. The message he brings isn't half bad either: it is childish and idiotic to destroy each other with nuclear weaponry. Who'd have thought we needed someone to tell us that? Given that we do, it's a good thing we had Klaatu to point it out.

3. E.T. from E.T.: The Extra-Terrestrial

Beating out Futurama's Nibbler as the most lovable alien on our list is E.T. He comes to Earth not as an invader, not as a scientific phenomenon, not as a messenger, but as a lost little boy who needs a friend to help him phone home. Trying only to have some fun and get back to his family, he is one of the few aliens on this list that we care about as much as we would a human character. His appeal is as simple as that.

2. Spock from the Star Trek franchise

In an era of cold war and, in science fiction, hostile and implacable aliens, Gene Roddenberry created the friendly and fascinating character of Mr. Spock. He was half Human and half Vulcan, but he disdained his human legacy and embraced the Vulcan people's values of completely subsuming their feelings in favor of an ethic of logic and peace. In the Star Trek TV series and films, he often served to make clear the logical option of a choice that Captain Kirk must make (while Dr. McCoy often represented the emotional option). Played brilliantly by Leonard Nimoy, who was able to show us Spock's fierce intelligence and his constant war within himself perfectly, Mr. Spock is one of the most significant and engaging characters, human or alien, in all of science fiction.

1. The Xenomorph from the Alien and Alien vs. Predator franchises

The best alien of all time comes from a movie titled simply Alien. Every characteristic of this alien is awesomely terrifying, not the least of which is the way he is born. In Alien this creature horrified us because we never knew where he was, but we always knew he was hunting us. In subsequent films, the xenomorph (named as such because it takes on some physiological characteristics of the animals it uses as procreation vessels) further proved himself to be perfectly designed for pure deadliness. This is a beast with both strength and speed, as well as a taste for blood, and his gothic design, thanks to H.R. Giger, is as cool and frightening a look as you could ask for. Just make sure you observe from a safe distance because in space, no one can hear you scream.