Cable used to symbolize everything wrong with the comics industry; now he's a fairly popular character, since he stopped being a Nineties Anti-Hero and gained more characterization than "uses huge-ass guns". It also helps that he was teamed up with one of Marvel's most popular characters, Deadpool.
An example of that gained characterization was when the writers finally came up with a reason for him to be more proactive (aka challenging norms publicly, doing much larger-scale, more-public things) in his work than Xavier. Originally, Cable was just "the guy who gets things done because whiny idealism like Xavier's doesn't work." A big reason he shifted was because people in the real world started disliking overly violent/murderous solutions to things. A real turning point was in Cable and Deadpool where Cable admitted that his need to change things in a big way now can very much be a flaw (Truth in Television too - people who go in trying to fundamentally change a system right away are usually kicked/laughed out very fast).
Damian Wayne, the son of Batman and Talia al-Ghul, initially came off as a Jerk Sue, violent, powerful, and a jerkass. But after he becomes the new Robin next to Dick Grayson's Batman after his father's death, many fans are surprised to find that he is becoming much more likable, thanks to some character development by Grant Morrison (his creator) and Paul Dini, who have effectively made him into the Tsundere youngest member of the Bat-Family who, despite his bravado, has grown to appreciate his new family (he has more-or-less grown to accept Tim Drake andStephanie Brown, and has admitted to preferring to work under Dick Than his father!) and has been told that there is much he still needs to improve on. But take notice that this is still at least a work in progress, as the fanbase at large has merely decided to changed their opinion from him being near universally reviled to seeing the character as a Base Breaker.
Probably the biggest part of rescuing him from the Scrappy heap was when he started acting more his age instead of trying to pretend he was older and more mature. There's one moment in particular between him and Dick Grayson that shows how he's starting to open up more, has come to truly respect Dick, and is willing to show his vulnerabilities. It happens after Dick, Damian, and Alfred realize that Bruce really is still alive, and are exploring secret parts of Wayne Manor to find clues Bruce left for them in the past.
Damian: If my father returns... we can't be Batman and Robin any more, can we?
Dick: No, I guess not. It's a small price to pay for getting him back alive.
Damian: What will I do? Do you think my father will let me stay on as Robin?
Dick: You honestly think he'd put up with you the way I do? [pause] ...Damian, I'm joking.
This is also a reason people liked Colin Wilkes aka Abuse: Damian was interacting with someone his own age without showing massive disdain for the person. He even fist-bumped him! Given as Damian clearly was supportive of Colin being Abuse, many are hoping for his return to continue to prove Damian isn't a total prick.
Similarly, Blackhawk's Chop-Chop started out as a rather horrendous "Chinaman" comic-relief stereotype (even, arguably, by the standards of its time.) Subsequent eras gradually improved the character. By the '60s, Chop-Chop was recognizably human, and by the '80s, he was a competent equal member of the team in the Evanier/Spiegle run, and a worldly, sophisticated, and articulate character going by the name Weng Chan in Howard Chaykin's re-tooling of the series.
Simon Furman goes too far with this in his Transformers comics, rescuing Grimlock from being a brute with no consistent characterization to a cunning if arrogant and temperamental warrior who cares just as deeply for his own troops as does Prime for all Autobots, and who only uses lines like "Me Grimlock" because he feels intellectuals don't get respected enough. Thankfully, he seems to have learned his lesson.
Some people think Furman's approach to Grimlock has come right around and done the opposite with Grimlock. This could be due to him enduring a bit of Wolverine Publicity.
IDW's Spotlight did this for Wheelie, not only emphasizing his survival skills to a near-Bad Ass level (remember, the kid did used to live on a planet full of Sharkticons), but also provided a plausible reason for his constant rhyming.
Drift was rescued from the Scrappy heap thanks to fan-favorite writer James Roberts including him in his new ongoing series, severely downplaying his brooding faction-switching swordsman tendencies in favor of playing up his trend as The Fundamentalist with his blind loyalty to the Circle Of Light and playing with his constant habit of delivering pseudo-philosophical speeches about war and morality by making him Rodimus's speechwriter. He's even being written as being flawed and still distrusted by many (and not in a "poor Drift gets no love but he should" way), with Ultra Magnus even considering his likelihood of returning to crime "off the scales".
Drift is a major case of a phenomenon you see a lot in comic books: a Mary Sue is hated by all but the writer, then the next writer gets his hands on the character and opinion turns around. Evidently, it takes someone who can step back and figure out where he fits and who he needs to be instead of the creator who can't get past his "I adore him, so, you must too, and I'll keep him onscreen 24/7 until you do!" feelings about his pet.
Matter-Eater Lad of the Legion of Super-Heroes started out as a total weirdo with an incredibly lame power who was eventually written out of the storyline, first by going back to his home planet and eventually going into a coma after saving the universe by eating a "Miracle Machine" that was warping reality. During the "Five Years Later" era, though, he was re-imagined with a rock-star persona (Cool Shades and all), gleefully reveling in his own absurdity.
"All this roughhousing is giving me an appetite * CHOMP* and you don't want to give me *gulp* an appetite."
Brainiac 5: (to restrained villain) Move anything, and he'll bite it off. (We then get a shot of Matter-Eater Lad with a big-ass grin on his face)
Not only does Peter David have a knack for this, he has a vocal preference for it. He's practically the patron saint of forgotten or tragically uncool X-Men. The entire cast of every iteration X-Factor is made up of C-list and D-List characters that no one else wanted. Under PAD's writing, they've all flourished and grown into their own.
Layla Miller debuted in House of M as an obvious plot device, to the point that fans nicknamed her Layla MacGuffin. When PAD recruited her onto the cast of X-Factor, he transformed her into an Oracular Urchin, Deadpan Snarker, and frequent Creepy Child, suddenly becoming a fan-favorite. Even after a big crossover punted her into the distant future, fan demand earned her a one-shot comic.
Kyle Rayner initially received a lot of hate from Green Lantern fans (mainly Hal Jordan fans) when he replaced Hal Jordan after the controversial Emerald Twilight arc. However, over time, Rayner was presented as a likable character, thanks to Grant Morrison's run on JLA. Fans argue that under Geoff Johns, Kyle lost a good bit of his limelight, but given that he's got his own book (as well as being the sole White Lantern), it seems that he's still in a good place.
Once Rayner's creator, Ron Marz, got through his period of making him as unlike his predecessors as possible, he also helped temper his previously brash character quite a bit.
Hard to believe, but in the early days of Chris Claremont's epic run on X-Men, a vocal group of fans wrote letters demanding that Wolverine be killed off (70s readers weren't ready for a Nineties Anti-Hero). It didn't help that co-plotter and penciller Dave Cockrum didn't like Wolverine either, focusing his attentions on his own personal creation, Nightcrawler. When John Byrne (a Canadian) replaced Cockrum, he liked the idea of a major hero from the Great White North, and became enamored of the little runt. A Crowning Moment Of Awesome or two later, and an Ensemble Dark Horse was born...
The filk-rock band Ookla the Mok have a song called "Arthur Curry" about what a lame hero Aquaman is. It includes the line "Not even Peter David can make me cool."
Virtually every character in Warren Ellis 's Stormwatch. Ellis deepened the characterization and turning the focus somewhat away from action. Ellis's run on the title is now considered one of the most important in comic book history and one of the best of the nineties. Most of the characters ended up dead anyway in the crisis crossover.
Daken was widely despised by the fanbase during his initial appearances in Wolverine Origins, but is starting to grow into a fan favourite after joining the Dark Avengers.
Ian Flynn's run on the Sonic the Hedgehog comic series has done this for a good number of characters. Some of these include turning Sonic's Evil Twin, err, Evil Sonic, into a more distinctive character named Scourge. He's also managed to do this for the almost universally despised Monkey Khan, turning him from an obnoxious Journey to the West parody into a more well rounded, sympathetic, and tragic character.
Though his degree of success is debatable, he is also blatantly trying to do this to Princess Sally, subverting her Positive Discrimination status by having more moments she admits to making a mistake. The bad blood received from slapping Sonic and breaking up with him in public also seems attempted to be rectified, with a couple of conversations where she discusses the situation with another, blatantly ashamed and remorseful over how she acted.
To a degree, Shadow the Hedgehog and Rouge the Bat. After their appearances for the Sonic Adventure 2 issue, they rarely appeared elsewhere and it seemed that Bollers and Penders had absolutely no idea what to do with them, relegating them to either background status or as villains. This was made even worse when there was no adaptation for Sonic Heroes, thus their more heroic natures couldn't be explored. It would take Ian's takeover to have them pull a Heel-Face Turn and later become the much beloved Team Dark.
The mainstream version has become quite popular, due to getting his own series, Scarlet Spider, giving readers an anti-heroic Spider-Man who is still heroic deep down, but struggles with his Dark and Troubled Past. Its cancellation saddened more people than you'd think... until they found out he was heading for the revival of the New Warriors.
The creation of the Marvel Adventures line saw a lot of characters getting a much-needed face lift, but by far, the best-received Re Tool was changing The Wasp into Giant Girl. Readers that hated the former loved the latter, and readers who liked the former adored the latter even more. Of all the characters who were axed when the MA: Avengers series was cancelled in favor of a continuity reboot in MA: Super-Heroes, Giant Girl was the one most fans were saddest to see go.
Superboy-Prime had, by Legion of Three Worlds, become a Villain Sue, a Straw Fan, and a positively colossal Jerk Ass. Then, there came Blackest Night, where he featured in a crazily metatextual story, became the butt of several massiveTake That, Scrappy! scenes, started receiving major repercussions, and was shown being almost heroic for once - trying to save the heroes of the DCU from getting killed off in the latest event, something you'd expect from a genuine fan. Some fans have since reevaluated him. Unfortunately, his next appearance put him back into has old Jerkass Villain Sue routine in the last issues of the pre-New52Teen Titans.
Red Hulk was introduced by Jeph Loeb taking down one major league hero or cosmic entity after another, with no particular motivation and a secret identity that no one cared about. He used to provide the page picture for Villain Sue. After Loeb lost control of the character it's been explained that his Villain Sue abilities were due to a Deadly Upgrade by a group that was using him to dispose of their enemies, then die. It's been removed, and Red Hulk is going through the process of being cathartically (to both readers and characters) beaten up by the people he trounced while in God Mode and facing up to the consequences of his actions. Commentators on his newer storyline have mentioned how it just feels weird to actually be interested in Red Hulk as a character.
A similar rescue has taken place with the Red She-Hulk. Originally she was introduced as a generic 'sexy bad girl', complete with giant guns and a ludicrously ripped costume, and a prime example of Loeb's inability to come up with good names. Since then the firearms and the torn outfit were unceremoniously dropped, instead putting her and the Hulk into a well-received two-person Love Quadrangle.
Maria Hill started off as Nick Fury's replacement after he went into hiding, and her main character trait seemed to be "Mega Bitch", specially in regards to superheroes and she became one of the poster children for what was wrong with the Pro-Registration side during the Civil War. Then upon giving up her position to Tony Stark, she was subsequently changed into a much more likable character, one of Tony's closest confidants and quite badass.
Invincible Iron Man rescued her for a lot of people, as she was given a backstory, character development, and ended up walking away from Tony when she discovered that he'd do Civil War all over again because he thought he was right. The run eventually led to Maria racing into the middle of Osborn's Dark Avengers to save Thor's life. Even if people don't like her, she's definitely not a Scrappy now.
Spider-Man: Ever since "Spider-Island", Carlie Cooper has slowly gained more fans as Peter's ex-girlfriend than she ever did while dating him. At first, she was a classic bad fanfic Mary Sue of the "perfect love for the main character because I say so" type. Then she got in the hands of a writer who wasn't basing her on his own daughter, got some character traits that weren't clippings taken from Gwen or MJ, and you can actually go a panel without everyone telling us over and over and over how perfect Carlie is for Peter even when they're the last characters you'd expect it from. By now, Carlie... almost makes people not see red at the mention of her name. (Her origin and the whole One More Day thing mean that'll be the best she can do for at least a few more years, though.)
Dan Slott's run rescued the Spider-Man comic itself from the Scrappy Heap. To begin with, many fans were driven away by the editorially-enforcedJ. Michael Straczynskistoryline where Peter trades his devoted supermodel wife toSatan in exchange for his sick, elderly aunt, and the following couple years were hardly well-received either, what with there being no consistent writer and Replacement Scrappies for both established villains and love interests (including the aforementioned Carlie) abounding. This era closed out with two storylines of questionable quality, one of which undid the sacred cow that was "Kraven's Last Hunt" and the other featuring the Lizard going bananas and eating his Morality Pet son alive. Sales plummeted. Slott, who came aboard the book immediately after the Lizard story, fixed things by being the one and only writer on the title, bringing back many classic villains, demoting Carlie from love interest to supporting character, and generally making the book a lot more fun. The only people he really catches heat from are fans of the Hobgoblin, due to the rather anticlimactic death he wrote for that character. And then of course it turned out he'd just set up his (previously-established!) twin brother to die in his place.
The early years of the Fantastic Four had the Invisible Girl be very much The Scrappy. It was even alluded to in the comic book itself much to Sue Storm's dismay and despite her team mates jumping to her defense. Come issue #22 and her invisible shields were introduced for the first time and she was rescued from the Scrappy heap...
Flamebird (formerly Bat-Girl) of the Teen Titans was one of the common characters to find on fans' "most hated Titan" lists due to her ditziness, her gaudy costume, and her one-sided obsession with Nightwing. Geoff Johns and Ben Raab attempted to make her a somewhat more serious fighter when she refused to accept Nightwing's demand for her to quit, and gave her a heavily revamped look. But this wasn't convincing for enough fans, as the character wound up back in limbo and was often just trotted out for crowd scenes. After her history with the Titans was erased in the New Fifty Two reboot, JH Williams' Batwoman series went back to portraying her as ditzy and clueless to the point where she was brutally stabbed and left in a coma for several issues. Since her healing, she's now taken on the name "Hawkfire" and sports a Darker and Edgier costume and attitude about crime-fighting. Time will tell if it sticks.
As of the New Fifty Two; it would appear Vibe of all people is getting this; getting a re-vamped backstory, a serious power-boost, membership in the new JLA and his own ongoing series. Not too bad for one of the long time contenders of "Worst Member of the Justice League EVER".
The Sentry was roundly despised outside of his original miniseries, being named the poster boy for Character Shilling, a massive God-Mode Sue, and a compulsive whiner with an inconsistent mental illness. His death didn't win him any favors, as more popular characters waxed poetic about good deeds he'd never performed on-panel. The Age of the Sentry miniseries ended up winning him a fair number of fans, primarily because it showed him actually doing the stuff everyone lauded him for, recasting him as a less dickish version of the Silver Age Superman. Unfortunately, since Age of the Sentry is pretty dubious in canon, plenty of fans didn't make the connection, and treat the likeable Sentry who teamed up with cavemen as basically a separate character from the one who ripped people in half.
The Superior Foes of Spider-Man has been doing this for a whole slew of c-list supervillains and superheroes by giving them fleshed-out backstories and personalities when they had once been generic, one-off crowd fillers or red shirts. Most notable with Mach VII (who wasn't a full on Scrappy, but no one cared about him), Boomerang (who's gimmick was viewed as lame), and the Looter (who was widely seen as nothing more than a Silver Age embarrassment).