Ares, Greek god of war, had been since The Silver Age of Comic Books nothing more than a lesser enemy of Hercules and Thor who nobody cared about. Then he got a mini-series in 2004 that strongly revamped his character, and later joined the Avengers. Since then multiple writers in multiple titles were working hard to make him win the fans' love. They succeeded so much that his death caused a backlash much stronger than the death of Wasp, founding Avenger.
Bob, Agent of HYDRA became quite popular for no particular reason when he first appeared in Cable & Deadpool and has gone on to become a fan favorite. Fan reaction to his appearance in Deadpool's solo title can be summed up as, "OMG, IT'S BOB!"
Obadiah Stane/Iron Monger from Iron Man. Between his debut in issue 163 and death in issue 200, he stands as one of the villains that managed to mentally screw up Tony Stark. You'd have to be a Darkhorse if you're the Big Bad of the first movie, despite your rather short time in the series.
Kid Loki from Journey into Mystery is pretty popular. Even after it's revealed that his entire life was essentially a "Shaggy Dog" Story, and his older self takes control of his body, he remained a very popular character. This lead to Loki gaining a role in Young Avengers, where the Kid Loki persona haunts Loki's subconscious. This, combined with MCU Loki's popularity, led to Loki getting his own ongoing series, Loki: Agent of Asgard.
Shocker while regard as a silly for many years has also become pretty popular due his unique (quilted) design, personality, and weapons.
Rodrick Kingsley is considered to be the true Hobgoblin and readers were quite pleased to see his return.
Toxin is also quite popular; a pity that Patrick Mullgan died and that Toxin is now bonded to Eddie Brock.
Mania from the Venom book is also quite surprising popular due to her background and design.
Mr. Negative and Overdrive are the only Brand New Day villains to stay.
Karn, the only good member of the Inheritors that is actually liked by fans largely for his tragic backstory, fun design, and especially for betraying theother Inheritors.
A lot of the new supporting cast members introduced by Dan Slott but especially Max Modell (for being a great Smart Guy for the Spiderfamily) and Anna Maria Marconi (for being really nice and her dwarfism being treated with impeccable good taste.
Sophia Sanduval from the Marvel Adventure Spider-Man. Generally down to earth, sweet, supportive of Peter/Spidey and a generally likable and entertaining companion a lot of people consider her one of Peter's best love interests behind only Mary Jane and Black Cat. So much so that when the series was eventually cancelled the biggest lament was that there would be no more Chat.
People really seem to love Ultimate Jessica Drew, Peter's Opposite-Sex Clone. She's appeared relatively only a few times in the Ultimate Marvel Universe. Yet fans tend to go "oh no!" whenever something bad happens to her or squeal whenever something good happens to her.
Moonstone was just another villain until Thunderbolts reinvented her as a Manipulative BastardJerkass. Then she had her own comic, was a part of the Dark Avengers team and sat at the right hand of Norman Osborn. Same with Songbird (helps that her hair tastes like strawberries).
Several of the background characters at the Xavier Institute developed fanbases despite having no or few lines, thanks to neat visuals or powers. Notable amongst these are Pixie, a girl with fairy wings and the ability to disperse a hallucinogenic powder (and who got a miniseries); and Anole, a lizard-like mutant with superhuman camouflage powers and a long tongue.
Both of these were introduced in New Mutants vol.2, which also has a different case - the initial cast were Wind Dancer, Prodigy, Elixir and Wallflower, who were later joined by Surge. After the book's relaunch as New X-Men: Academy X, they got a rival team in the new Hellions. Once Craig Kyle and Christopher Yost took over the series, they decided to focus on the most popular characters. Which were Surge and two thirds of the Hellions.
Under the hand of Peter David, Shatterstar has been the subject of extensive online debate, beaten up The Thing, kissed almost as many people as the rest of the cast put together, been featured prominently in at least three different covers, made himself a very likely candidate for a limited series, and just generally stolen the spotlight both in-universe and out; all this in, what, ten issues or so? Not bad for a character who the writer refused to allow anywhere near the book for quite some time.
Peter David took a bunch of nobodies, and made them into a team in the much beloved X-Factor series, specifically the one centering around X-Factor Investigations. The biggest examples would be Jamie Madrox, the Multiple Man, and Layla Miller, who went from The Scrappy of the House of M event to one of the series' most popular characters.
Among X-Statix's frequently rotating cast, few stood out as much as the team's teleporter, U-Go Girl, a cute blue-skinned Southern Belle with a Tear Jerker of a backstory and probably the most functional moral compass among the Unscrupulous Hero team. Writer Peter Milligan was well aware of her popularity and chose to herald a major turning point in the story by killing her off - years later, reflecting on the series, he considered doing that his biggest mistake. But with Jonathan Hickman's X-Men gaining the means to bring mutants Back from the Dead, it's only a matter of time until U-Go Girl makes her long-awaited return.
Speaking of Jonathan Hickmans X-Men House of X has brought Cypher (whose often been regarded as one the lamest X-Men by far due his near useless Omniglot powers) newfound popularity. Thanks to Cypher being the one who can speak and translate for the living island Krakoa where all Mutants residing making him one of the most important Mutants alongside Xavier, Moira MacTaggert and Magneto. Cypher even appeared following comics teaming up the likes of Nightcrawler and Magik.
Miss America Chavez. Despite her rather minor role, her new Civvie Spandex outfit became popular with cosplayers before the series even started and towards the end of the series even Kieron Gillen admitted that from fandom output and the way she somehow worked her way into the center of later covers, he feels like she is the character his run will be remembered for the most.
Tommy is consistently the least developed member of the team, but is well liked by most of the fans, to the point that his lack of development is something of a sour point for many. He's also Kate's most popular hetero pairing, despite the two not actually officially hooking up (though had quite a lot of Ship Tease and appeared to hook up at the end of Vol 2).
Broo, a mutant member of the Brood Alien race that causes problems for the X-Men. After a small appearance, he vanished until Wolverine and the X-Mencame onto the comic book scene, where he ended up being one of the series' most popular characters, and one of their most popular students. Kid Gladiator, another alien, also gets a lot of love.
Many of the characters who came to be reintroduced in mid-90s revival series also 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.
A lot of GCPD officers and detectives such as Renee Montoya, Harvey Bullock, Crispin Allen, and Jason Bard are extremely popular, sometimes even being considered part of the Batfamily.
A bunch of the more obscure Batman Inc./Club of Heroes members are really popular with fans such as Batwing, El Gaucho, Nightrunner, and Batcow.
Black Mask is frequently cited as an example of a great Batman villain who is woefully underused. Maybe it's his cool look or maybe it's his Xanatos-style intelligence, but in any case fans seem to really like the guy. Him getting Hijacked by Ganon in Arkham Origins just caused much of the fanbase to clamor even harder for him to get a day in the limelight.
Killer Croc is very well-loved when he's written as a Noble Demon. In the New 52, he got a big popularity boost after his sympathetic portrayals in Batman Eternal and Gotham Academy, which paint him as someone who just wants to protect those he cares about.
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.
Golden Age example: 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.
This is similarly true of many JSA members of that era. Hourman, 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.
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.
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.
Arkillo has fast become one as well thanks in no small part to the massive amount of character development he received.
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.
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 Darkhorse, 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.
Static 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. Strong fan love for fellow Milestone Comics characters 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 afterward.
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 from Teen Titans. She lasted little more then 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.
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 Awesome 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.
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 shes inevitably and hilariously the fixation of Thanoss 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.
Raul the Cat, from American Flagg!. He even won the Comics Buyer's Guide Fan Award for "Favorite Supporting Character" in 1984.
Archie Comics: A later comic had Sabrina switch everyone's gender. Fans really want more of Reggie's counterpart, Regina, who is a proper Alpha Bitch.
Archina and especially J.J. are very popular (a picture of them and Regina can be found here◊). Archina has cute Girlish Pigtails and people enjoy her reverse harem more than the usual version, while J.J.'s fashion choices, apathetic personality, and Big Eater qualities make her attractive to people (much more so than normal Jughead).
Kevin's debut issue sold out in record time. While this could have been due to the publicity over Kevin being the first openly gay character, issues where he is prominent consistently sell better than average, especially if he's on the cover, to the point that he got his own spinoff in less than a year.
Battle Chasers: Red Monika. Even though the comic might be obscure these days, she is the main reason why anyone still remembers it due to the amount of pin-ups and fan art spawned by it, which is ironic, considering she was a secondary character to Garrison and Gully, who were the story's point-of-view characters.
G.I. Joe's Snake-Eyes. The character created only so that the company could sell another figure without having to pay to paint it ended up becoming the posterboy for the franchise as a whole.
Patty (and by extension, her gaming group, Patty's Perps) is very popular with the fans. It seems that almost every issue includes at least one request from fans for "More Patty!"
Crutch (who is, incidentally, a member of Patty's group) has amassed a respectable fanbase of his own. Readers responded well to the sympathetic portrayal of his criminal past, and his determination to keep his nose clean. The awesome Crime Nation the RPG campaign he started running helped matters.
Gordo has his fans, mostly for his unshakable niceness, even in the face of Stevil's constant bullying. And he has one kickass home gaming setup, complete with special lighting, aromatherapy machines, and a sno-cone maker.
Bug from the Micronauts was originally just the Plucky Comic Relief on the team but as time went on, he became a more sympathetic three dimensional character. Along with his own one shot comic, he also got to appear in non-Micronaut titles such as Guardians of the Galaxy and according to Word of God, he came very close to being in the movie.
He's the most despicable character; a real shitbag. He enjoys torture, and readers can't get enough," said Azzarello. "In one of Lono's earliest appearances, he had a woman tied to a bed and raping her! I figured that should solidify him as 'the bad guy'. But I guess not.
Sonic the Hedgehog (Archie Comics): Scourge the Hedgehog and, by extension, the Suppression Squad. When they first appeared, Scourge was just "Anti-Sonic", the Suppression Squad the "Anti-Freedom Fighters" and their homeworld of "Moebius" was just "Anti-Mobius". Even their looks were bland - they were just "Freedom Fighters in leather". Anti-Sonic was so ineffectual, his lowest point was being dropped by Antoinecompletely by accident. Under the pen of Ian Flynn, however, he shed all of those traits, getting a new look and taking a breaking speech to heart, becoming a massive threat.
In Wildguard "Freezerburn" was originally going to die in #4, but the series site poll showed him to be one of the most popular characters. Crag Langley was dispatched instead. Freezerburn ultimately won the poll, out of a very big field of applicants, to become a member of the final team.
Nikolai Dante was, by a fairly wide margin, voted to appear on the cover of prog 2000, in spite of the series only having run for three years at the time and pushing aside long time fan favorites like Hammerstein and Sláine.
Sinister Dexter was hugely popular during its run, sometimes running twice in the same prog, and the ending of the series made prog 1139 the first prog since prog 2 that did not have any Judge Dredd in it.