| Name | Source | Type |
|---|
| Kafers | 2300 AD | Humanoid |
| Kaleds | Doctor Who | Humanoid |
| Kalish | Farscape | Humanoid |
| Kaalium | Moontrap | Cyborg |
| Kal-Kriken | Utopia | |
| Kalliran | C. J. Cherryh's Alliance-Union universe | |
| Kambuchka | Ascendancy | |
| Kanamit | To Serve Man Twilight Zone and Short Story | Humanoid |
| Kang and Kodos | The Simpsons | Squid-like. Green, single-eyed squids intent on conquering Earth |
| Karemma | Star Trek | Humanoid |
| Kat Nebulans | Kid vs. Kat | Cat-like aliens from Kat Nebula. |
| Kariak | Haegemonia: Legions of Iron | |
| Kats | Kid vs. Kat | cybernetic, cat-like aliens from the planet Kat Nebula. |
| Kazon | Star Trek | Humanoid |
| Kdatlyno | Larry Niven's Known Space | |
| Kerbals | kerbal space program | |
| Kerons | Sgt. Frog | |
| Kess'Rith | Renegade Legion | reptilian rhino-like centauroid |
| Key-Guardians | Utopia | |
| Kheirosiphon | Adventure Time: Fionna and Cake | |
| King Ghidorah | Godzilla films | Three-headed dragon |
| Kineceleran | Ben 10 | Armored velociraptor-like humanoids from the stormy planet Kinet, Kinecelerans have extraordinary speed, able to accelerate to 500 miles per hour in a second. They can use their speed to generate twisters and also have prehensile tails and sharp claws. |
| Kisshu | Tokyo Mew Mew | |
| Kharaa | Natural Selection | |
| Kherubim | Wildstorm | |
| Khunds | DC Comics | Humanoid |
| Khurtarnan | Farscape | Humanoid |
| Kif | C. J. Cherryh's Chanur novels | |
| Kig-yar | Halo | |
| Kilaaks | Destroy All Monsters | |
| Kilrathi | Wing Commander games | |
| Kizanti | Battlelords of the 23rd Century | Humanoid |
| Kimera | Earth: Final Conflict | |
| King Cold | Dragon Ball Z | Humanoid; Reptilian |
| Kivar | Roswell | |
| Klaestronian | Star Trek | The Federation visited the planet Klaestron in 2339 to mediate the Klaestronian Civil War. (DS9 episodes "Dax", "Second Skin") |
| Klackons | Master of Orion | |
| Klaxuns | 2300 AD | |
| Kleer Skeleton | Serious Sam: The First Encounter | |
| Klingons | Star Trek | Humanoid |
| KMT 184.05 people | My Love from the Star | Humanoid; including Do Min-joon |
| Knnn | C. J. Cherryh's Chanur novels | |
| Koala Bear People | Adventure Time | an alien species like koala and bear |
| Koozbanians | The Muppet Show | |
| Korath | Galactic Civilizations II: Dark Avatar | |
| Korbinites | Marvel Comics | |
| Korvax | No Man's Sky | Humanoid; machine |
| Korx | Galactic Civilizations: Altarian Prophecy | |
| K-PAXians | K-PAX | |
| Kra'hen | Imperium Galactica II: Alliances | |
| Krakeds | Battlelords of the 23rd Century | |
| Kraylor | Star Trek | Humanoid |
| Kree | Marvel Comics | Humanoid |
| Kreel | Star Trek | |
| Kreely | Schlock Mercenary | |
| Kreetassan | Star Trek | |
| Krell | Forbidden Planet | |
| Krellepem | Harry Turtledove's Worldwar series | An aquatic animal native to Home. Their uncanny physiology resembled Earth's extinct trilobites and they were implied to be less evolved. Krellepem are treated as a delicacy by the Race in which special tools are required to break their shells, especially since the Race could not even suck the meat out of the shells as humans could do. |
| Krenim | Star Trek | |
| Kriken | Metroid Prime Hunters | |
| Krishnans | L. Sprague de Camp's Viagens Interplanetarias Series | Green skinned humanoids with antennae. |
| Krith | Richard C. Meredith's Timeliner Trilogy | |
| Krogan | Mass Effect | |
| Krolp | Harry Turtledove's Vilcacamba | Centauroids larger than horses with tiger-like stripes, heads similar in shape to a jack-o'-lantern with jagged jaws, and have a strong odor that similar in smell to Limburger cheese. |
| Kromaggs | Sliders | |
| Kronn | Area 51 and its sequel | One-eyed insectoid. Able to mutate humans, turning them into zombies, cling on walls, and fires some sort of energy. |
| Kroot | Warhammer 40,000 | |
| Krynn | Galactic Civilizations II: Dark Avatar | |
| Krynn | The Journeyman Project 2: Buried in Time | |
| Krynoids | Doctor Who | |
| Kryptonians | Superman | Humanoid |
| Kryten | Red Dwarf | Series 4000 Mechanoid |
| KS-2 | Adventure Time: Distant Lands | Rabbit-like humanoid, Y5's mom |
| Kssthrata | Schlock Mercenary | |
| K'tang | Star Control 3 | |
| Ktarian | Star Trek | |
| Kulturan | The Sinusoidal Spaghetti | |
| Kweltikwan | Lilo & Stitch | Characterized by a large, rotund figure, four yellow eyes, dark blue-ish/purple skin tones save for pink on their front torsos, palms, and faces on dark pink on distinctly rimmed eye sockets, large wide mouths with blue tongues, blunted fangs, and small noses. |
| Kylothians | Men in Black | |
| Kymellians | Marvel Comics | Humanoid body with horse's head |
| Kymera | Fortnite Battle Royale | A level 1 outfit in the Chapter 2: Season 7 Battle Pass. |
| Kymnar | FTL:2448 RPG | |
| Kyo | C. J. Cherryh's Foreigner series | |
| Kyrie | Heroscape | Humanoids with wings |
| Kyulek | O.R.B: Off-World Resource Base | |
| Kzinti | Larry Niven's Known Space series and Star Trek: The Animated Series | Felinoid - large bi-pedal tigers. Male: Kzintosh, Female: Kzinrett. Aggressive space-faring carnivores, with sub-sapient females |