Many of the characters who came to be reintroduced in mid-90s revival series experienced this sort of status. Chief among them Animal Man and the Doom Patrol (both reimagined by Grant Morrison), The Sandman (to the point where most people outside of comics don't even realize how deeply ingrained DC continuity is in this character's history), Kid Eternity and of course Starman.
The New 52 revival of Dial H saw two major popular characters. First was Boy Chimney, the first hero Nelson dialed in the first issue, an eccentric, lanky figure with a hide as tough as bricks and the ability to create and manipulate smoke. He would later be joined by Open Window Man, a superhero in his own right and one of the only members of the Dial Bunch to get any significant panel time (including an entire issue devoted to him). And that was at the point where the series was being cancelled. Two things helped Open Window Man: 1) he was the crime fighting partner of Boy Chimney back when he was alive, and 2) because his origin reveals that he's basically Batman but with a window theme.
The Red Tornado was originally introduced as "Ma" Hunkel, a supporting character in "Scribbly the Boy Cartoonist," but was so outrageously silly that she completely overshadowed the title character. 60 years later, Ma was the curator of the Justice Society of America museum, and nobody remembers poor ol' Scribbly.
Wildcat. A lot of modern fans don't realize that in the 40s, Wildcat was just barely a member of the JSA, participating in exactly two JSA stories of the time. He became more popular during the 70s JSA revival and All-Star Squadron, and then really took off in the modern series. It helps that he's one of the few remaining living team members.
Heck, the JSA as a whole is this. Hourman, the Sandman Dr. Mid-Nite and others were completely failed concepts that would likely have vanished forever if not for their JSA links - which allowed future writers to bring them back in future storylines. Both had further runs, and currently popular successors.
Martian Manhunter has never hold a solid series and just tends to bounce between whatever comic has room for him. However, his status as The Heart of the Justice League, his varied array of powers and the interesting background he comes from make him a favourite among fans. When he was removed from the Justice League founding line-up in The New 52 fans were pissed, to put it lightly.
The Flash: The original Golden Age Flash, Jay Garrick. The guy doesn't develop much in his modern appearances, and he's largely a supporting character even within the beloved JSA series. But you'll find nobody, from Flash fan to wider DC fan, who doesn't just love the old man. He's theCool Old Guy in the DCU, and a father figure to several generations of heroes. He's also one of the nicest guys alive, and even fellow heroes love the guy.
Flash villain turned ally Pied Piper has developed a fan following since he was reinvented in the late 1980s as one of Wally West's closest friends. Piper also came out as one of the first openly gay characters in comics, in an issue that won a GLAAD award.
Mia Dearden was Put on a Bus until very recently, but her quirky personality, tragic backstory and positive representation of sex workers make her very liked by fans.
This has happened to a few members of the Green Lantern Corps.
In the 80s, it was Kilowog, who's still a fun character and a foil to the four Earth Lanterns. Recently, it's Mogo the living planet, who was introduced in the 80s and then rarely used until Green Lantern: Rebirth. He's had a lot to do since then, including being a key being in Infinite Crisis and the Sinestro Corps War storylines.
Ganthet. The only non-Lawful Stupid Guardian on all of Oa. Had the Fridge Brilliance moment of realizing that when a Lantern's hopeful, their will exponentially increases. Hence why he's the man.
Saint Walker became one almost instantely due in no small part how nice and wholesome the guy is.
Arkillo has fast become one as well thanks in no small part to the massive amount of character development he received in New Guardians.
Alan Scott is strikingly popular, despite having essentially nothing to do with the modern mythos and often not even existing in the same universe. Every comic he shows up in gets wide praise, and he seems to have little to no hatedom relative to the other human Lanterns.
Jonah Hex of All Star Western. His book was one of the highest rated books, and the lowest selling, of the New 52.
Captain Cold is one of the least seen Legion of Doom members in this alternate universe miniseries, but both the methods and attitude he sports while engaging in Cut Lex Luthor a CheckPhoto Op with the Dog heroics stand out.
Elasti-Girl doesn’t appear until more than halfway through the story, but her The Big Guy moments in Alex Ross's art style make her decently remembered and very notable.
Scarecrow is one of the more generic villains in the story and only has a handful of action scenes, but his The Blank mask and the scope of his Mad Scientist efforts make him highly memorable.
Solomon Grundy The Brute has even less personality than usual, but his fearsome appearance and occasional Smarter Than They Look moment (such as being one of the only villains to escape at the end of the story) make him a highly notable villain.
The Metal Men are tertiary characters at best, but the way they use their liquid alloy powers to give the Justice League impressive battle suits makes them deeply appreciated parts of the miniseries.
Legion of Super-Heroes started out as a one shot appearance in Superboy. They caught on and eventually edged him out of his own comic. The Legion itself is not lacking in Darkhorses; in fact it's hard to find a character that doesn't have a solid fanbase, Chemical King and the Legion of Substitute Heroes most notably. The biggest example of an ensemble darkhorse for the Legion of Super-Heroes is Wildfire; originally a one-shot character who dies in his first appearance, fan response to the character led to the writers bringing him back and make him team leader, after the fan-voted leadership election for the year he joined the team had him win. Though he's largely been absent from the book since the 1989 "Volume Four" reboot, he has a vocal fanbase that has kept the character at the forefront of the property. Like that other facelessEnsemble Dark Horse, part of Wildfire's appeal is his unique design.
The Night of the Owls storyline introduced several Talons, assassins of the Court of Owls who attacked many members of the Bat Family. Most haven't been seen since and are in cold storage, but the one who attacked Batgirl, a victim of Japanese air balloon bombing in World War II, returned for the Batgirl Annual and has joined the Birds of Prey as Strix.
In the '80s Will Payton version of Starman, his sister Jayne and mother Jo Marie were more popular with fans than Starman himself or any of the villains.
Milestone Comics is an Ensemble Dark HorseUNIVERSE, chief among them being Static, who maintains a lot of fans, despite his comic being one of the first New 52 titles to be removed and his long absence from television. In Young Justice, he is one of the most hailed characters in the trailers. Other Milestone favourites are Rocket, Icon, Xombi and Hardware is also this.
Supergirl's Earth-2 counterpart Power Girl also qualifies due to being one of the most well-knownsex symbols in DC Comics (there is a good reason she is the trope image for the comic book sub-page), even though she is not considered a A-list superhero nor really focused or used much, but she still has her very devoted fanbase regardless.
Bizarro. Only appears every once in a while and rarely plays a major role in the story, but beloved for his goofy and lovable personality, plus his at-times legitimately tragic nature. Notably, he died in his very first appearance, decades ago, but fan outcry resulted in him being reborn via Applied Phlebotinum soon afterwards.
Mr. Mxyzptlk, mainly for always being really funny whenever he shows up.
Krypto the Superdog. Cheesy maybe, but the dog is so brave, loyal, and just plain fun that he'll always be a welcome part of the Superfamily.
Terra. She lasted little more than a year in the comic, but is one of the most well-recalled characters in the series. A "different version" of her (who might or might not have been the original with amnesia) was brought in a few years later only to eventually be killed off and replaced by a THIRD one, who became the Best Friend/sidekick to Power Girl, then went on to befriend Starfire in Starfire (2015).
Aqualad was Put on a Bus early on, but his good looks and cute relationship with Dolphin make him beloved by many.
While the short-lived comic The New Guardians has been largely forgotten, Linkara'sreview of the second issue gave special attention to one character: Snowflame, a Crazy Is Cool one-shot villain who derives superhuman strength from snorting massive amounts of cocaine, which he verbosely revels in and hails as his god. Two crack-addled rants and a beatdown later, he becomes Linkara's favorite character, and now commands a significantly larger fanbase than any of the heroes.
And although he only made one comic appearance he lives on through frequent appearances in Atop The Fourth Wall and his own Webcomic.
The Legend of Wonder Woman (2016) version of Etta Candy has become very popular and arguably the most well-known aspect of the already well-received miniseries. It helps that unlike most versions after the Golden Age, she is neither slim nor does she feel particularly insecure about her weight, being simply a modern take on her original Big FunAction Girl version.
Artemis of the Bana-Mighdall. Introduced as an Anti-Hero Substitute of Diana in the '90s, Artemis was killed off but resurrected due to her popularity as a Foil to Diana. She has since become the most focused and developed member of the Bana-Mighdall tribe and is considered one of the most iconic Wonder Woman supporting characters.
Nubia has gained a bit of a following for being the first black Amazon character in the Wonder Woman universe and being the most prominent one next to Philippus. This popularity eventually lead to her becoming a much more prominent character in DC Rebirth and eventually taking over as queen of the Amazons. She even got her own ongoing for a time.
Ferdinand, Diana's minotaur chef, is the most memorable supporting character from Greg Rucka's run.
Death from The Sandman. She was originally meant to be a minor recurring character who might appear a handful of times, but her instant popularity with the audience — helped no doubt by her perky, upbeat, kindhearted nature, a sharp contrast to most personifications of Death — was so strong that Gaiman made sure she'd get at least one appearance in all ten volumes. These appearances vary in size but always feel substantial, and their sparsity helps prevent the story from ever focusing on her too much. Not to mention she's become canon in the actual DC universe. Death has even made at least two cameos in the Marvel Universe where she’s inevitably and hilariously the fixation of Thanos‘s lust, much to her distaste.
Watchmen has a flock of these in the form of the Minutemen. Also a good deal of the villains that are mentioned offhandedly, most notably the Twilight Lady. Perhaps more notably, Rorschach is much, much more popular than Alan Moore intended.
of the second issue gave special attention to one character: Snowflame, a Crazy Is Cool one-shot villain who derives superhuman strength from snorting massive amounts of cocaine, which he verbosely revels in and hails as his god. Two crack-addled rants and a beatdown later, he becomes Linkara's favorite character, and now commands a significantly larger fanbase than any of the heroes.