| Name | Source | Type | | Caitian | The Animated Series | Feline humanoid |
| Calamarain | Star Trek |
| Caleban | Frank Herbert's Whipping Star | invisible telepathic beings who are actually the minds of stars |
| Calcinite | Terror from the Deep |
| Callineans | Star Fleet | Humanoid |
| Calvin | Life | Cephalopod-like |
| Caliban | C. J. Cherryh's Alliance-Union universe |
| Capelons | Ascendancy |
| Conductoid | Omniverse | Black-skinned aliens from planet Teslavorr, they are cycloptic humanoids with plugs on their fingers, prehensile tail, and antenna on their heads. They have the ability to absorb energy and redirect it as electrical energy that they can control to a great extent. |
| Cardassian | Star Trek | Reptilian Humanoid |
| Star Trek | Reptilian Humanoid |
| Carggites | DC Comics Legion of Super-Heroes |
| Carrionites | Doctor Who | Humanoid |
| Cat | Red Dwarf | Felis Sapiens. Evolved over the course of three million years in deep space, from a domesticated housecat. |
| Catbug | Bravest Warriors | A combination part cat and part ladybug, Catbug simultaneously exists in two dimensions; reality and the See-Through Zone. |
| Cathar | Star Wars | Cat-like humanoid |
| Catkind | Doctor Who | Feline Humanoid. |
| Cat People | Marvel Comics | Feline humanoid |
| Catalyte | Utopia |
| Catteni | Anne McCaffrey's Catteni Series |
| Cavalier | Tommy & PJ |
| Cazare | Ratchet & Clank |
| Celareon | Frontier Wars |
| Celatid | UFO Defense |
| Celestials | Marvel Comics |
| Celestialsapien | Ben 10 | A race of aliens from the Forge of Creation, these beings resemble horned humanoids with a body similar to that of a starry night sky. They are immensely powerful and can make their thoughts reality, but are limited by their psyche: their minds are divided into separate beings that need to agree in order to do even simple tasks. |
| Centauri | Babylon 5 | Humanoid |
| Centrans | Christopher Anvil's Pandora's Planet stories | Feline humanoids |
| Cerebrocrustaceans | Ben 10 | Crab-like aliens from Encephalous IV with massive heads due to super-sized brains. They are extremely intelligent (their IQ is at one nonillion), though not as smart as Galvans, and can use their enhanced intelligence to perfectly calculate the trajectory of objects and operate complicated machinery, and also generate and manipulate electricity into electric blasts and force fields. |
|
| Ceti eel | The Wrath of Khan | bug-like ear parasites from Ceti Alpha V |
| Chaethe | Kathy Tyers's One Mind's Eye |
| Chalnoth | Star Trek |
| Chamachies | Ascendancy |
| Changeling | Star Trek |
| Chaos | Independence War, aka I-War, and Edge of Chaos |
| Charrids | Farscape | Humanoid |
| Chasch | Jack Vance's Planet of Adventure Series | Big headed humnoids divided in subspecies. |
| Chatilian | Battlelords of the 23rd Century | Humanoid |
| Cheblons | Alliances |
| Cheela | Dragon's Egg | inhabitants of neutron star |
| Chelonians | Doctor Who novels |
| Chenjesu | Star Control | Crystalline life-form |
| Cherubs | Homestuck | Cherubs are characterized by their green exoskeleton. |
| Chevanno | Utopia |
| Chi | C. J. Cherryh's Chanur novels |
| Chigs | Above and Beyond |
| Chimera | Fall of Man | Reptilian Hybrids between virus and host |
| Chimera Sui Generis | Ben 10 | Green-skinned squid-like humanoids from the planet Vilgaxia (formerly known as Murray), while they themselves are fairly nonviolent, one of the most dangerous intergalactic warlords, Vilgax, is of this species. They are shown to have the ability to turn into monstrous squid-like beings when submerged in water. |
| Chinger | Bill, the Galactic Hero |
| Chiss | Star Wars | Blue-skinned red-eyed humanoids |
| Chmmr | Star Control |
| Cho-choi | Jack McDevitt's Infinity Beach |
| Chozo | Metroid | Bird-like species. Extremely technologically advanced and spread out across the galaxy. |
| Chronian | Race Against Time | Looks just like a human. They have vast Time manipulation powers and able to create Energy beams. |
| Chronomyst | Ascendancy |
| Chryssalid | UFO Defense |
| Cinnrusskin | James White's Sector General series |
| Cirronians | Tracker |
| Cizerack | Battlelords of the 23rd Century |
| Clairconctlar | Star Control 3 |
| Clutch Turtles | Liaden universe |
| Cocytans | The Dig | Furry, bird-like beings trapped in "Spacetime Six", a parallel universe. |
| Coeurl | The Voyage of the Space Beagle by A. E. van Vogt | Similar to a big cat; prehensile tentacles sprouting from shoulders. Feeds on potassium and/or organic phosphorus. |
| Cognocenti | Star Trek |
| Colatas | Farscape | Humanoid |
| Cole | Tracker |
| Colonists | The X-Files |
| Colour out of space | H. P. Lovecraft |
| Coluans | DC Comics Legion of Super-Heroes |
| Combine | Half-Life 2 | an alien empire; note: many of the "Combine" seen in the game are actually humans that have been assimilated or collaborate as brutal police troopers. |
| Coneheads | Saturday Night Live | Humanoid with conical heads |
| Control Brains | Invader Zim | The Control Brains assign the Irken race with roles and are the unspoken leaders of the Irken Empire. |
| Coola (Cooler) | Dragon Ball Z | Humanoid; Reptilian |
| Coreeshi | Farscape | Humanoid |
| Coridanite | Star Trek | Humanoid |
| Corporal Giroro | Sgt. Frog |
| Corvallen | Star Trek | Reptilian Humanoid |
| Cosmo the Seedrian | Sonic X | Human Plant |
| Covenant, The | Halo | Collective of alien species who are allied with each other, Composed of Grunts, Brutes, Elites, Hunters, Jackals, and Prophets. Religious Hierarchy with intent to destroy the Human Race. |
| Cranassians | Raiden | Hi-tech aliens that has control over red crystals with unlimited powers, which are used to power up their weapons and equipment. |
| Cragmite | Ratchet & Clank |
| Creators | The Jupiter Incident |
| Crites | Critters films | carnivorous hairballs |
| Cryons | Doctor Who | Humanoid |
| Ctarl-Ctarl | Outlaw Star |
| Cthulhi | Cthulhu Mythos |
| Cthulhu | Cthulhu Mythos |
| Cybermen | Doctor Who | Marauding cybernetic life-forms. Originally an alien race driven to conversion by catastrophic climate change, more recently reimagined as assimilated humans. |
| Cybertronians | Transformers | Large robots from planet Cybertron able to change their shape at will into other mechanical constructs, most commonly varying types of vehicles like planes and trucks. Known more commonly as Transformers. |
| Cybyota | Orion's Arm |
| Cyclons | Metroid series |
| Cylons | Battlestar Galactica | Sentient robots. Remnants of a civilization of reptilian aliens (also known as Cylons) in the original series, but created by humans in the remake series. Both mechanical and biological flesh-and-blood versions co-exist, with the biological versions in charge. |
| Cynoid | Master of Orion III |
| Cyrollan | The Journeyman Project |