For a lot of science fiction fans, a big part of what makes the genre so great is the aliens. And because they're limited only by the writers’ imagination, aliens run the gamut from cute and fluffy to terrifying and murderous. Even in a series like Star Wars, aliens can be cute and fluffy like the Ewoks or slimy and dangerous like the dianoga.

They can be humanoids or giant blobs, enemies or allies, but they almost always add something interesting to the mix.

Here are the 14 Most Memorable Alien Species in TV and Movies.

14. Poleepkwa: District 9

You remember those crazy bug-like creatures. In the movie, humans refer to them using the derogatory term “prawns,” but not because they look like seafood. It’s the people of Johannesburg, South Africa who coin the term, after a local species of cricket called the parktown prawn. They’re memorable largely because they’re just so creepy.

They’re large, technologically advanced insectoids who eat raw meat and love cat food, which affects them similar to the way catnip effects cats. After one of their ships hovers for months over Johannesburg with no signs of activity, a team of humans enter the ship and discovers the sick and malnourished aliens. The humans bring them to Earth and provide them with health care, but confine them to District 9, a government camp inside the city. Soon, it turns into a slum, as conflict breeds between the humans and the extraterrestrials.

13. Symbiotes: Spider-Man 3

Of course, the Symbiotes originated in the comics, but in the movie world, they turn Peter Parker (Tobey Maguire) into the most obnoxious version of himself. They’re basically alien parasites that bring out the host’s dark side, and when one of them merges with Peter, it turns him into a total ass-hat. He breaks Eddie Brock’s (Topher Grace) camera and tries to make Mary Jane (Kirsten Dunst) jealous by turning up at the club where she works with Gwen Stacy (Bryce Dallas Howard). So much drama.

He even tells his friend Harry Osborn (James Franco) that his father Norman, a.k.a. Green Goblin, never loved him (not that Harry is such a likable character, but Peter’s comment is a little below the belt). Eventually, Peter removes the Symbiote, which then attaches itself to Brock, transforming him into the villain Venom.

12. Predators: Predator series

Probably one of the most iconic alien species in movies. They’re creepy in a completely different way from the Poleepkwa, and they’re called "predators" for a reason. They know how to stalk their prey and stay hidden (by staying invisible), and the titular alien hunts humans for sport.

After tracking Dutch Schaefer (Arnold Schwarzenegger) and his elite special forces team through a South American jungle – and taking a few of them out along the way – Dutch and the predator come face to face. Apparently, not even the super strong, strategic, and murderous alien is a match for Arnold’s raw strength. After an intense fight, Dutch cripples the alien, who won’t let Dutch have the satisfaction of killing him, and so it self-destructs.

11. Xenomorphs: Alien series

When it comes to just the sheer grossness factor, these guys probably take the cake. Remember that scene where one of them breathes its hot breath just inches from Ripley’s (Sigourney Weaver) face? Eww. Even their babies are ugly.

While they demonstrate some problem-solving ability and the capacity to learn new skills, they’re not as intelligent as humans, but they’re largely driven by their predatory nature and the desire to use human hosts to reproduce, so they’re pretty terrifying. In Alien: Resurrection, things get even more disturbing when a human-xenomorph hybrid joins the mix. It has facial features that hint at human emotions, but retains a lot of the scary physical features of the original xenomorphs.

10. Daleks: Dr. Who

They may be villainous, but they’re kind of cute, right? Like evil R2D2s. According to Wikipedia, they resemble “human-sized pepper shakers” – and that’s a pretty accurate description. The Daleks are cyborg aliens bent on conquering the universe and destroying any other species they see as inferior (which is basically every other species).

Their catch phrase, “Exterminate!” isn’t exactly subtle. They were created by a scientist named Davros, who genetically modified some of his own people, the Kaleds, and integrated them with a robotic shell. Inside the robotic shell, the creature is soft and kind of gross-looking. Davros also removed all of their emotions except for hate (what could possibly go wrong?).

9. Jawas: Star Wars franchise

In some ways, the Jawas are kind of like the Ferengi of the Star Wars universe. They’re all about making a quick buck. They sell equipment that’s often shoddily refurbished, and they scavenge the debris from podracer crashes and downed ships in order to re-sell the parts, and sometimes swindle their customers.

The difference, though, is that the Jawas have always seemed more mysterious than the Ferengi. What are they hiding under those hoods? They did help to reunite C-3PO and R2-D2 on Tatooine, so that’s one thing working in their favor. But, they promptly took advantage of the situation and sold the droids to Luke’s (Mark Hamill) uncle Owen.

8. Flora Colossus: Guardians of the Galaxy 

The most famous of his species is Groot (Vin Diesel). There’s a meme that says something like, “I may not know much, but I can recite every line of Groot’s in Guardians of the Galaxy.” It’s funny because all the character is able to say is “I am Groot,” but the phrase can mean anything he wants it to depending on the context. But what Groot may lack in vocabulary, he makes up for with heart.

The Flora Colossus is a generally humanoid species, but their tree-like body structure makes them nearly invulnerable to physical harm. They also have an accelerated healing factor, and they can regrow their entire bodies from just a small twig.

7. The Na’vi: Avatar

Aesthetically, the Na’vi are probably among the most elegant aliens in movies and TV. They’re blue and they stand about 10 feet tall. Although they’re hunter-gatherers and not particularly advanced technologically (they’ve probably reached the equivalent of the humans of Earth’s Paleolithic Era), they’re highly advanced in other ways.

They have a sophisticated spiritual connection to Pandora, the lush jungle moon that is their home. Their respect for the natural world is at the center of their culture, which is very much at odds with the agenda of the movie’s human characters. And this is the very lesson that Neytiri (Zoe Saldana) tries to teach to Jake (Sam Worthington).

6. The Q: Star Trek franchise

The Q are an immortal, omnipotent species of aliens who live in the Q Continuum. They can instantaneously teleport and time travel, and they have the ability of matter-energy transformation. The Q have evolved over a very long period of time, and eventually came to see themselves as the ultimate form of evolution. Therefore, many of them developed a certain apathy toward life, believing they had already experienced everything they could experience.

The Q don’t have individual names, and are all called “Q.” The most famous member of the species (John de Lancie) makes multiple appearances on The Next Generatio (as well as Voyager), in which he often unexpectedly learns an important lesson about the nature of life through the mortal crew of the Enterprise. One of the major story arcs of the show involves him holding humanity on trial, essentially believing he has the right to determine the fate of the species.

5. Ewoks: Star Wars franchise

The Ewoks have always been a little controversial – it seems like you either love them or hate them. Some fans find them friendly and endearing, and enjoy the David vs. Goliath aspect of the teddy bear-like creatures’ ability to stand up to the Empire. Others think they’re too “cutesy” for Star Wars, and find it unrealistic that they could combat the Empire, with all of its technological advancement.

But, as adorable as the Ewoks are, they’re not all sugar and spice. They’re carnivorous creatures, and initially plan to eat Han (Harrison Ford), Luke, and Chewbacca (Peter Mayhew) in Return of the Jedi. There's even a fan theory that they ate all of the defeated stormtroopers after the battle of Endor. But whatever your opinion of them, the Ewoks are certainly among the most recognizable of the Star Wars species.

4. The Borg: Star Trek franchise

The Borg are among the most terrifying alien species in movies and TV. They have the strength of cyborgs, they’re highly advanced technologically, and they lack compassion or any desire to compromise or negotiate. They compose a collective of individuals of many other species who have been abducted and modified with cybernetic implants in order to be assimilated into a large, interconnected hive mind. Individuals operate only as drones, with the exception of the Borg Queen (Alice Krige). They strive for perfection, and believe that incorporating the knowledge of other species will help them achieve that.

As such, their singular goal when interacting with other species is to assimilate them and turn them into drones. Their catchphrase is, “Resistance is futile.” Picard even had a brief stint as a drone. One of the most notable members of the Borg is Voyager’s Seven of Nine (Jeri Ryan), who is liberated from the Collective and, with the guidance of Captain Janeway (Kate Mulgrew), learns to appreciate her humanity and individuality.

3. Wookiees: Star Wars franchise

Wookiees might look pretty intimidating – and they are indeed very strong physically – but they’re also highly intelligent and loyal. They’re fast learners and often adept at using advanced technology. Their language is called Shyriiwook, and while they can understand other languages, due to the structure of their vocal chords, they can’t speak them.

Their home planet is a lush jungle world called Kashyyyk. George Lucas has said that his dog, Indiana (also the namesake of Indiana Jones), was the inspiration for the appearance of the Wookiees. Of course, the most famous Wookiee is Chewbacca, Han’s longtime friend, partner in crime, and copilot.

2. Vulcans: Star Trek franchise

We all know the Vulcans as a calm, rational species. In fact, it’s this characteristic that makes the dynamic between the half-human, half-Vulcan Spock (Leonard Nimoy) and the brash and sometimes impulsive Kirk (William Shatner) so great. But Vulcans weren’t always so cool under pressure. Once upon a time, they were a very violent species. As a result, they adopted the moral code of the philosopher Surak, making logic their guiding principle and suppressing their emotions.

However, some Vulcans, like Enterprise’s T’Pol (Jolene Blalock), carry their emotions closer to the surface. T’Pol even explores the potential benefits of experiencing emotion in a deeper way, and develops a relationship with her human crewmate, the lead engineer Trip Tucker (Connor Trinneer).

1. Klingons: Star Trek franchise

The Klingons are possibly the most widely recognized Star Trek species. They’re kind of like space Vikings. They’re warriors, and their most prized value is honor. They’re definitely not the type of aliens who are apt to talk about their feelings. If you watch old episodes of Star Trek, you’ll see that the Klingons basically just looked a lot like Snidely Whiplash – villainous, mostly human-looking aliens with dark hair and pointy eyebrows.

But in the 1979 movie Star Trek: The Motion Picture, they’re given forehead ridges, a weird continuity issue that isn’t explained until a 2005 two-part storyline in Star Trek: Enterprise. The episodes “Affliction” and “Divergence” explain that, in an attempt to mimic experiments by humans intended to create augmented soldiers, Klingon scientists used human genetic material on their own people, resulting in a pandemic of more human-like Klingons.

Of course, the most famous Klingon is TNG’s Lieutenant Worf (Michael Dorn), who was raised by human parents. He holds various positions but is most known for his role as Chief Security Officer on the Enterprise.

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Can you think of any other memorable alien species who should be on this list? Let us know in the comments!