| Name | Source | Type |
|---|---|---|
| M-113 Creature | Star Trek | |
| Macra | Doctor Who | Huge crustacoids who feed on noxious gases that are deadly to humans. |
| Magic Man | Adventure Time | Martian; after magic seem to have been transferred to Betty, Simon's fiancée, he turned Magic Man into "Normal Man". |
| Magma | Ultraman Leo | Saber Tyrant |
| Magog | Andromeda | |
| Magolor | Kirby's Return to Dream Land. | |
| Mahendo'sat | C. J. Cherryh's Chanur novels | |
| Maians | Perfect Dark | |
| Majat | C. J. Cherryh's Alliance-Union universe | |
| Malons | Star Trek | |
| Mangalores | The Fifth Element | Thick-skinned humanoids; warriors and weapon specialists. Considered savage and brutish by other races. |
| Mantis | Conquest: Frontier Wars | |
| Mantis Man | Adventure Time: Distant Lands | |
| Mantrins | Titan A.E. | Kangaroo-like aliens with large, powerful back legs; native to Solbrecht. The character Stith is a Mantrin. Also called Sogowans. |
| Margles | Adventure Time | Martian; once Magic Man's wife |
| Marklars | South Park | Orange-skinned aliens with egg-shaped heads and yellow eyes. They refer to all people, places, and things as "Marklar". |
| Marmosians | Ascendancy | |
| Marro | Heroscape | Skinless creatures with insectoid social organization |
| Martians | H. G. Wells' The War of the Worlds | Tentacled and very intelligent and technologically advanced. Attempted to take over Earth as Mars became less and less habitable for them. |
| Martians | Edgar Rice Burroughs's Barsoom series | Humanoid |
| Martians | Marvin the Martian from Looney Tunes and Duck Dodgers | |
| Martians | Premendra Mitra's Mangalbairi (The Martian Enemies) | |
| Martians | Ray Bradbury's The Martian Chronicles | Humanoid |
| Martians | Adventure Time | Humanoid |
| Martians | Aelita (1924 movie) | Humanoid |
| Martians | Mars Attacks (Topps trading cards) and Mars Attacks! (Tim Burton movie) | Skeletal humanoids with massive craniums and a twisted sense of humour |
| Martians | Quatermass and the Pit | |
| Martians | Larry Niven's Known Space | |
| Martian Manhunter | DC Comics | |
| Marvelous Man | The Guardians of Justice | Alien superhero; parody of Superman |
| Marvin | Marvin Marvin | |
| Marzoids | Invader Zim | |
| Masari | Universe at War | A sentient race of ancient Atlantians that are human-like in appearance. |
| Masters | The Tripods | |
| Mazians | Battlelords of the 23rd Century | |
| Mebes | Ascendancy | |
| Mechanon | Star Frontiers | sentient mechanical race created by the Eorna |
| Medusans | Star Trek | |
| Meehooks | Fusion comic book series | dinosaurs with fur |
| Meekrob | Invader Zim | Pure energy beings. Meekrob was set to be conquered by Invader Tenn until she received a shipment of malfunctioning SIR Units giving away her location and thus angering the Meekrob, creating further tension between the Meekrob and the Irken Empire. |
| Meklars | Master of Orion | |
| Melconians | Keith Laumer's Bolo series | canine-like humanoids |
| Melmacians | ALF | |
| Melnorme | Star Control | |
| Melotians | Melonpool | |
| Memory Donk | Bravest Warriors | The Memory Donks are a species of "old-lady"-like beings that take away the memory of anyone around them. |
| Menoptra | Doctor Who | |
| Mentors | Doctor Who | |
| Merseians | Technic History by Poul Anderson | |
| Merewifs | Bravest Warriors | Merewifs are a race of mermaid-like creatures. Most notably, Plum |
| Mesklinites | Hal Clement's Mission of Gravity | millipede-like |
| Methorians | Barrington J. Bayley's Zen Gun | gaseous giant-giant dwellers |
| Metroid | Metroid series | A creature that, in its infancy, resembles a jellyfish-like creature capable of siphoning the life force of other creatures, using this to kill them. As it grows, it undergoes two metamorphoses, the first one making it similar to an arthropod, and the second one making it resemble a quadrupedal theropod dinosaur. They were created by the Chozo to be used as weapons against the more dangerous X parasite. |
| Metrons | Star Trek | |
| Mewmans | Star vs. the Forces of Evil | |
| Micros | Brain Plague by Joan Slonczewski | Microbial aliens that inhabit the brain and offer their host new abilities. |
| Microman | Microman | |
| Micronoids | X-Com: Apocalypse | Sentient parasitic bacteria |
| Minbari | Babylon 5 | Crested humanoids; a small number have telepathic abilities |
| Minions | Ascendancy | |
| Minosians | Star Trek | |
| Mintakans | Star Trek | |
| Miradorn | Star Trek | |
| Misha | Battlelords of the 23rd Century | Humanoid |
| Miu Miu-miu | My Lover from the Planet Meow | Cat-like humanoid |
| Mmrnmhrm | Star Control | |
| Mnemonoid | Adventure Time | Only in comic version |
| Mon Calamari | Star Wars | |
| Mondoshawan | The Fifth Element | Humanoid |
| Monoids[broken anchor] | Doctor Who | |
| Mogadorians | Lorien Legacies | Humanoid, warlike race intent on destroying the Loric and invade Earth. Described as having very pale skin and dark hair and eyes. |
| Moon Dragons | Bravest Warriors | Moon Dragon toenails are used to make the Bravest Warriors' space suits. |
| Moonflowers | Hanazuki: Full of Treasures | Childlike creatures with Mood plumes resembling flowers, they live on moons that don't orbit planets. |
| Mooninites | Aqua Teen Hunger Force (individually: Igninokt and Err) | Pixelated-liked aliens |
| Mork | Mork and Mindy | |
| Morlocks | H. G. Wells' The Time Machine | |
| Morlocks | Larry Niven's Known Space | |
| Morok[broken anchor]s | Doctor Who | Humanoid |
| Mor-Taxans | War of the Worlds (TV series - first season) | |
| Morthren | War of the Worlds (TV series - second season) | |
| Movellans | Doctor Who | Humanoid robotic conquerors; fought a war with the Daleks |
| Moxx of Balhoon[broken anchor] | Doctor Who | Blue, large-headed humanoid |
| Mri | C. J. Cherryh's Faded Sun trilogy | Humanoid |
| Mr. Saturn | EarthBound | |
| Mrrshan | Master of Orion | |
| Mudokons | Oddworld series | |
| Mugato | Star Trek | |
| Mukadil Paejua | Vampire Idol | Vampire-humanoids |
| Mutons | X-COM: UFO Defense | |
| Mutzachans | Battlelords of the 23rd Century | Humanoid |
| Muuh | Orion's Arm | |
| Mycon | Star Control | |
| The Mysterons | Captain Scarlet and the Mysterons |