S
- Sabretooth in Iron Fist #14
- Sandman in Amazing Spider-Man #4
- Sarcen in Punisher War Journal #25
- Sasquatch in Uncanny X-Men #120
- Satana in Vampire Tales #2
- Sauron in X-Men #60
- Scarecrow
- as Ebenezer Laughton in Tales of Suspense #51, March 1964
- as Straw Man in Dead of Night #11, August 1975
- Scarlet Witch in X-Men #4
- Scarlet Spider (Benjamin Ben Reilly) in The Amazing Spider-Man #149
- Scorpion in The Amazing Spider-Man #20
- Sebastian Shaw in Uncanny X-Men #129
- The Sentinels in X-Men #14
- Sentry in The Sentry #1
- Serpent Crown (as Helmet of Power) in Tales to Astonish #101
- Serpent Squad in Captain America #163
- Sersi in Eternals #3
- Seth in Thor #240
- Shatterstar in New Mutants #99
- She-Hulk in Savage She-Hulk #1
- Shiva in Wolverine (vol. 2) #50
- Shock in Daredevil #314
- Shocker in The Amazing Spider-Man #46
- Shuma-Gorath in Marvel Premiere #5
- Siege in Deathlok #19
- Sif in Journey into Mystery #102
- Silver Sable in The Amazing Spider-Man #265
- Silver Surfer in Fantastic Four #48
- Silverman in The Amazing Spider-Man #73
- Sin in Captain America #290
- Siryn in Spider-Woman #37
- The Skrulls in Fantastic Four #2
- Slapstick in Slapstick #1
- Slayback in Deadpool #4
- Sleepwalker in Sleepwalker #1
- Slug in Captain America #325
- Songbird
- as Screaming Mimi in Marvel Two-in-One #54
- as Songbird in Incredible Hulk #449
- Speedball in Amazing Spider-Man Annual #22
- Sphinx in New Warriors #4
- Spider-Girl in What If...? #105
- Spider-Man in Amazing Fantasy #15
- Spider-Woman
- I: Jessica Drew in Marvel Spotlight #32
- II: Julia Carpenter in Marvel Super Heroes Secret Wars #6
- III: Mattie Franklin in Spectacular Spider-Man #263
- Splice in Wonder Man # 4
- Spymaster
- I: in Iron Man #35
- II: in Iron Man #254
- Squadron Sinister in Avengers #69
- Squadron Supreme in Avengers #85-86
- Starfox (Eros) in Iron Man #55
- Starhawk in Defenders #27
- Stark Industries in Tales of Suspense #40
- Stilt-Man in Daredevil #8
- Stingray
- as Walter Newell in Tales to Astonish #95, September 1967
- as Stingray in Sub-Mariner #19, November 1969
- Storm in Giant-Size X-Men #1
- Stranger in X-Men #11
- Strong Guy in New Mutants Annual #1
- Stryfe in New Mutants #87
- Sunfire in X-Men #64
- Super-Adaptoid in Tales of Suspense #82
- Super-Skrull in Fantastic Four #18
- Surtur in Journey into Mystery #97
- Swordsman in Avengers #19
Read more about this topic: List Of First Appearances In Marvel Comics Publications