M
- M in Uncanny X-Men #316
- Maa-Gor in X-Men #10
- MACH IV (as Beetle) in Strange Tales #123
- Machine Man in 2001: A Space Odyssey #8
- Mad-Dog (as Robert "Buzz" Baxter) in Amazing Adventures #13
- Madame Masque
- as Big M in Tales of Suspense #97
- as Whitney Frost in Tales of Suspense #98
- Mad Thinker in Fantastic Four #15
- Maelstrom in Marvel Two-In-One # 71
- Maggia in Avengers #13
- Maggott in Uncanny X-Men #345
- Magik in Giant-Size X-Men #1
- Magma in New Mutants #8
- Magneto in X-Men #1
- Magus in Strange Tales 175
- Major Victory in Marvel Super-Heroes #18
- Makkari in Eternals #5
- Malevolence "Mephisto's Daughter" in Guardians of the Galaxy #7
- Man-Beast in Thor #135
- Man-Thing in Strange Tales #1
- Man-Wolf (John Jameson) in The Amazing Spider-Man #124
- Mandarin in Tales of Suspense #50
- Mantis in Avengers #112
- Marlene Alraune in Incredible Hulk #11
- Marvel Boy (Noh-Varr) in Marvel Boy #1
- Marvel Girl (Jean Grey) in X-Men #1
- Marvel Man (Quasar) in Captain America #217
- Mary Jane Watson in The Amazing Spider-Man #25
- Mastermind in X-Men #4
- Master Mold in X-Men #15
- Master Order in Marvel Two-in-One #2
- May Parker in Amazing Fantasy #15
- Maximus in Fantastic Four #47
- Medusa in Fantastic Four #36
- Meltdown in Secret Wars II #5
- Meggan in New Mutants Annual #2
- Mentallo in Strange Tales #141
- Mentor
- I: A'lars in Iron Man #55
- II: android in X-Men #107
- Merlin
- I: Black Knight Comics #1; (modern) Strange Tales #134
- II: Journey into Mystery #96
- III: Captain Britain #1; (American) Marvel Team-Up #65
- Mephisto (comics) in Silver Surfer #3
- Micromax in Excalibur #44
- The Mindless Ones in Strange Tales #127
- Mimic in X-Men #19
- Mirage in Marvel Graphic Novel #4
- Mister Hyde in Journey into Mystery #99
- Mister Sinister in Uncanny X-Men #221
- Misty Knight in Marvel Team-Up #1 (named in Marvel Premiere #20)
- Mockingbird (Barbara "Bobbi" Morse-Barton) in Astonishing Tales #6, June 1971
- Huntress in Marvel Super Action #1, January 1976
- Mockingbird in Marvel Team-Up #95, July 1980
- MODOK in Tales of Suspense #94
- Mojo in Longshot #3
- Mole Man in Fantastic Four #1
- Molecule Man in Fantastic Four #20
- Molten Man in The Amazing Spider-Man #28
- Moon Knight in Werewolf by Night #32
- Moondragon in Iron Man #54
- Moonstone
- I: in Captain America #192
- II: as Moonstone in Incredible Hulk #228
- II: as Meteorite in Incredible Hulk #449
- Morbius, the Living Vampire in The Amazing Spider-Man #101
- Morg in Silver Surfer # 70
- Moses Magnum in Giant Size Spider-Man # 4
- Ms. Marvel in Marvel Super-Heroes #13
- Motormouth in Motormouth #1
- Multiple Man in Giant Size Fantastic Four #4
- Mutant 2099 in Mutant 2099 (one-shot)
- Mysterio in The Amazing Spider-Man #13
- Mystique
- I: as Raven Darkholme in Ms. Marvel #16
- II: as Mystique in Ms. Marvel #18
Read more about this topic: List Of First Appearances In Marvel Comics Publications