Marvel Universe
- Doctor Strange was a surprisingly effective bad guy. In 1963's Tales of Suspense #41, he easily defeated Iron Man and made a successful getaway when his too-honest daughter freed the hero. And he was never seen again! The name was later applied to Steve Ditko's unrelated magician.
- His whereabouts would finally be revealed almost 60 years later, in 2021's The Marvels.
- The final issue of The Last Defenders had Kyle Richmond retire from crime-fighting and pass the Nighthawk mantle to a young S.H.I.E.L.D. agent named Joaquin Pennyworth. Joaquin only ever appeared as Nighthawk in an obscure mini-series called Vengeance (written by the same writer as Last Defenders) and then never showed up again, with Richmond returning to the Nighthawk identity in later books. Bizarrely, Fear Itself: Fearsome Four implied that Joaquin had somehow stolen the identity from Richmond without his consent, even though that is not at all what happened.
- Kasper Cole became the new Black Panther in the last year or so of Christopher Priest's run and then starred in the short-lived Spin-Off, The Crew, before completely vanishing off the face of the Earth. (A decade and a half later, he briefly reappeared in Ta-Nehisi Coates' run).
- Kasper's teammate, Josiah X, also pretty much vanished into thin air. Ditto for Josiah's nephew Eli Bradley aka The Patriot from Young Avengers, who disappeared after Avengers: The Children's Crusade. He only briefly reappeared for a cameo in Marvel Comics #1000... then promptly disappeared again.
- When Brian Michael Bendis left Daredevil, the titular character had been imprisoned in one cell block with Kingpin, Owl, and Jigsaw. New writer Ed Brubaker removed Jigsaw, without any explanation.
- Spider-Man: Often happens to the supporting cast after all bigger changes of status quo. High school classmates from his early years, college classmates and associates, co-workers from the Daily Bugle, associates from various other occupations, and some of his love interests, vanish without explanation and are rarely mentioned afterward. A decent example is Joy Mercado, a female reporter who was depicted as one of Peter Parker's closest associates from 1985 to 1993. She made a few cameos in the rest of the 1990s, as the Daily Bugle was de-emphasized at the time, and has since vanished without a trace.
- Happens with ridiculous regularity in the X-Men books, especially once Xavier's Institute became a full-fledged school with a student body beyond the active team members, only getting worse after the "Decimation" event reduced the mutant population to around 200 (prompting the X-Men to try to get literally every mutant on Earth to live at the X-Mansion and, later, Utopia). Whenever a new writer takes over, you can count on at least half the extended cast quietly vanishing. Sometimes a later writer will remember them and either mention where they got off to or reveal that they have been there all along, but never really doing anything.
- Following Excalibur #67, half the team is Put on a Bus. Former members show up sporadically in other titles, except Feron.
- When the Micronauts began appearing starting in 1996 issues of Cable, not only was their reappearance due to a very apparent retcon, but no mention was made of Acroyear or Huntarr. Acroyear's absence is most likely due to the fact that Marvel no longer has the rights to any of the Micronaut characters derived from the old-school toyline. It doesn't explain why Huntarr is not there, as he was created by Marvel writer Bill Mantlo.
- The Mighty Thor: Remember Sigyn? Loki's wife (like in mythology)? Neither does anyone else, except as an Author Avatar in some Loki fanfics. Sigyn is presumed to have died in Ragnarok, but so did all the other Asgardians. Everybody else reincarnated, so the reincarnated Sigyn should be around somewhere. But nope, still no mention of her. See here.
- Wiccan of the Young Avengers originally had two younger brothers, who have since fallen off the face of the earth.
- Marvel Boy (formerly the Protector) had a girlfriend named Annie while he was a member of the Avengers. They had a very close relationship, and there were even some dangling plot threads concerning their relationship when Bendis left the book. Then came the second volume of Young Avengers, where Marvel Boy was shown shacking up with Kate Bishop without even a single mention of Annie. This was eventually explained. Marvel Boy dumped Annie at some point between The Avengers and Young Avengers, eventually leading to her apparent return as an Ax-Crazy Woman Scorned.
- Echo, Daredevil's former Love Interest, was once a member of the New Avengers briefly before disappearing, then briefly reappearing in Secret Invasion, then disappearing again. This wasn't lost on writer Brian Michael Bendis, who had Spider-Man question where she was at one point and have her flip her shit at Luke Cage and Jessica Jones when she reappeared after Siege and was asked to be Danielle Cage's babysitter."You know I used to be on this @#$@#$ing team!"
- Echo has turned up in Ta-Nehesi Coates' Captain America run as one of Sharon Carter's "Daughters of Liberty" team. Which is interesting, since Bendis had killed her off WHILE explaining where she'd disappeared to in his Moon Knight run. (Undercover trying to bring down the Count Nefaria mob.)
- Annihilation: Conquest introduced a character called Wraith, who seemed to have been created purely because his powers were useful to the plot. Once he had served his purpose in the story, he never appeared again, leaving his subplot (his quest to find the signet-ring-wearing man who killed his father) unresolved to this day.
- Wraith finally reappeared over a decade later in the pages of Guardians of the Galaxy (2019) (as a result of an admitted case of Creator's Favorite on the part of Donny Cates), instead searching for information on the Exolon possessing him, and was killed off the following year in the run-up to King in Black.
- Peter Porker: The Spectacular Spider-Ham introduced Mary Jane Waterbuffalo as this continuity's version of Mary Jane Watson, but she disappeared after "The Pig from Porker's Past, Part 1", an unresolved story featured in the 224th issue of the second volume of Marvel Tales. Instead of being brought back for the Spider-Ham story featured in issue four of Amazing Spider-Man Family and the Spider-Ham 25th Anniversary Special one-shot, Mary Jane Waterbuffalo was replaced with a new character named Mary Crane Watsow.
- Champions: Mark Waid's final arc of Champions (2016) saw Ironheart, Red Locust and the new Wasp, Patriot and Falcon join the team. While Ironheart and Wasp remained when Jim Zub took over the series, Falcon, Red Locust and Patriot all vanished without explanation.
- A number of Marvel Comics villains have rather inexplicably disappeared.
- Kala, Queen of the Netherworld was one of Iron Man's earliest foes. She has appeared sporadically since this, but her rapid aging when leaving her realm limits her appearances to situations where she's forced out of it by Subterranean politics, most recently during the Subterranean Wars in the 1990s.
- A somewhat peculiar case is Timeshadow, a member of the super-villain team Alliance of Evil. The others members of this 1980s super-villain team include the fan-favorite Frenzy (who has had over 30 years of appearances since then), the sympathetic villain Stinger (who was reintroduced decades later as a supporting character for the X-Men), and the thug-like Tower (whose death was an important plot point in a 1993 storyline). Timeshadow has never been seen since 1988, and he has since received only brief mentions which point out that nobody is certain of what happened to him. Out-of-universe, writer Fabian Nicieza has speculated that neither the writers, nor the editors found Timeshadow to be particularly likeable.
- The Ultimates: Petra Laskov first appears as Swarm, a member of the Liberators, and then as the second Wasp. She never appeared again since she killed Red Skull.
- Combat Kelly and his Deadly Dozen: Emory 'Snake-Eye' Simpson never appears after the first issue.
- Figment: Chimera, a pink, giant, dog-like creature that becomes an ally to Blair/Dreamfinder and Figment in the first series, is nowhere to be found in the sequel Figment 2: The Legacy of Imagination.
