Or just making him incredibly charismatic and allowing him to present his own account of his fall. What better way to show the seductive power of evil than by making the greatest villain in Christianity actually seductive to the reader? However he was not intended as entirely sympathetic, even he points out his Motive Decay, finally he just wants to upset God by causing the Fall of Man.
Murtagh from Inheritance Cycle has a vast following in the fandom. He's frequently referred to as the "real hero" of the Cycle. Please note that this didn't apply until after his Face-Heel Turn.
Galbatorix and Sloan. Galbatorix has hardly done a single heroic thing in the whole series. He appoints sociopaths as his generals and he has human-eating beasties do his bidding. To those who give Eragon the Ron the Death Eater treatment, Galbatorix is a hero. Sloan is somewhat more justified because he did wrong only to save his daughter; even Eragon gave him some respect in the end.
Mrs. Coulter and Lord Asriel in His Dark Materials. Granted, they're AntiVillains, but many people are willing to completely ignore the questionable, cruel, and downright evil things they have done.
Admirers of Asriel in the film canon can almost be excused; the one truly inexcusable thing he does, literally sacrificing his daughter's best friend to open the gate between worlds, was shifted to the (then) as-yet-unmade (and subsequently cancelled) sequel.
Petyr 'Littlefinger' Baelish in A Song of Ice and Fire. Charming, handsome, witty, always cheerful and a Manipulative Bastard with Chronic Backstabbing Disorder to boot. His ultimate goals are rather unclear, as is just how much of the anarchy and war that dominates the books has been orchestrated by him, but he has taken credit for the majority of it and its implied to be little more than Despotism Justifies the Means. Whilst the character is definitely subject to Alternative Character Interpretation and has many hidden depths to his personality, corners of the fandom treat him like a divine savior whose goals are all working to the benefit of the small folk, the people the wars have screwed over the most. Not to mention, they also "forget" how he forces unwanted kisses on his teenage niece-by-marriage Sansa Stark, his disciple and possible candidate for Queen, how he personally murdered his wife, Lysa Arryn and was responsible for the deaths of Jon Arryn and Ned Stark and how he forced an 11-year-old girl Sansa's friend, Jeyne Poole into prostitution.
As it turns out, there is also a small portion of the fandom that has decided, against all evidence, that Cersei Lannister is a tragic heroine trapped in abusive relationships with Jaime (in which she is the abuser) and Robert (okay, they got this one right). While it's true that her life hasn't always been a bed of roses, and Robert was undeniably a very abusive husband, this doesn't even come close to absolving Cersei of guilt for the monstrous crimes she herself has committed.
Tywin Lannister has a fair amount of fans, who admire his talent for scheming and take as Word of God his brother's assessment that while a harsh man, he was no harsher than necessary, and acted for the good of the family/realm. However, regardless of any positive outcomes of his actions, Tywin is shown to be totally unempathetic and treats everyone as pawns in his current scheme. Moreover, the circumstances of Tywin's death basically imply that he was just a hypocrite, and that Tywin's adoring brother Kevan was deluded by love for his brother into seeing good that wasn't there. In fairness, Kevan and Genna knew what Tywin was, they just loved him for being their brother.
Genna: Every little girl needs a big brother to protect her, and Tywin was big even when he was little.
Puddy. Despite knowing pretty much nothing about her backstory or inner thoughts, her fans on the story's forum seem absolutely certain that she had a rotten home life and that this makes her a Jerkass Woobie who just needs a hug. Don't mind her various assaults on the hero, her attack on the series' actual Woobie, or her abusive and bigoted attitude.
"The Man". He's only appeared in three short flashback stories involving the protagonist's mother as a child. In the first one, he nearly drowns her. In the second, he tries to seduce her. In the third, he impregnates her at the age of 15 and is confirmed as a Man EatingDemon. The reader reactions range from "Damn, he's smooth!" to "Let's wait to see some real evil before we judge him."
Joren from Tamora Pierce's Protector of the Small quartet got this for a while - in canon, he's radiantly beautiful to the point of being a Pretty Boy but also petty, bullying, sadistic and homophobic. He exists to bully the heroine, stage a few hazings, half-assedly attempt to befriend her and die in a closet. He's received the Draco Malfoy treatment in fanfiction quite a bit, when he's written about at all. Despite how this would probably disturb the author resoundingly, he's usually paired off with the heroine.
Raistlin Majere of the Dragonlance novels may qualify as this, although he's been a protagonist in some of the novels. He's definitely evil and creepy, yet he has a massive collection of fangirls.
Heathcliff in Wuthering Heights has received this treatment over the years, having become something of an archetype of the tortured-but-dashing Gothic Romantic Hero With A Heart Of Gold, up there with Mr. Darcy from Pride and Prejudice and Mr. Edward Rochester from Jane Eyre. This completely overlooks the fact that, within the novel, he's presented as a repellent, violent, and obsessively vindictive bully who spitefully destroys everyone who ever looked cross-eyed at him... and then, when they're dead, immediately does his best to destroy the lives of their children instead.
For that matter, Rochester has received some of this over the years as well; however, whilst he's certainly no saint, he's arguably presented with enough Laser-Guided Karma for his misdeeds and expresses enough genuine regret for his actions to at least slightly redeem himself in the eyes of the reader, unlike the largely unrepentant Heathcliff (whose karmic payback, whilst present, is a bit more oblique).
Emily Brontė may have foreseen this reaction when she created Isabella Linton, a silly teenager, who insists on perceiving Heathcliff as a Gothic Romantic Hero even though everybody around her tells her he isn't. It takes him hanging her pet dog before their elopement and then a few months of an abusive marriage to get this idea out of her head.
Discussed In-Universe in Thomas Hardy's The Return of the Native, when describing Eustacia Vye, the narrator mentions "At school, she used to side with the Philistines in several battles, and had wondered if Pontius Pilate was as handsome as he was frank and fair." Though the point is this is probably to show us that Eustacia is a Villain Protagonist and we're not meant to sympathize with her.
William Hamleigh in Pillars of the Earth, a spoiled and sadistic noble, whom, when his peasants cannot pay their taxes, rapes their wives and daughters as compensation. For some reason, certain fangirls wish that their fathers couldn't pay the taxes so they could suffer the same fate.
Dracula pretty much popularized the concept of Vampires Are Sex Gods. Which is thoroughly disturbing considering in the original novel, he was never portrayed as anything other than a hideous monster devoted to killing everyone and everything.
Most of the males in the Black Jewels series fit this trope. Daemon and his father Saetan are literally written to be walking sex, and are given sympathetic backstories and valid reasons to be total bastards. But they're still murderers.
Then there's Scourge, the leader of BloodClan. His fans tend to come in two varieties: Those who think he's a Badass, and those who pity him due to his rough childhood. However, the latter group is mostly made up of Misaimed Fandom - the author's note included in The Rise of Scourge specifically says that in writing the story they were trying to explain Scourge's evil behavior, and establish him as a Foil to Firestar, not justify what he did. In fact, when Scourge's abusive siblings - Socks and Ruby - come to Scourge after being abandoned by their owners, Scourge seems to have gotten over their bullying enough to simply have them chased away, rather than getting any sort of revenge on them. The fact that he continues to be evil despite having got over what originally made him one shows that his rough childhood doesn't excuse him for his atrocities.
Mapleshade gets this too due to having been exiled from ThunderClan for having a RiverClan mate, then getting kicked out of there as well when the kits drown. Despite this, though, she subverts this trope because she said that she earned her place in the Dark Forest and calls herself an irredeemable bitch.
To a certain extent, Thrawn from the Star Wars Expanded Universe. Yes, Timothy Zahn made him and the other Imperials complex and generally admirable. He wasn't evil, not black-and-white. But he was very ruthless, pragmatic, and above all, Imperial. He wasn't above You Have Failed Me, even if he needed more of a reason and was more forgiving of crew who weren't at fault. He lied, he was willing to hand Leia and her unborn twins to Joruus C'baoth, and he kept the Noghri in indefinite servitude with the lie that when he finished repairing their homeworld, they'd be free. Often, though, he's portrayed purely as someone who did what he had to do and chose to become a Necessary Evil.
The author of The Pendragon Adventure may have made Saint Dane too magnificent for his own good. While he isn't described as particularly attractive in his default form, it's become strangely common for fanart to depict him as a lithe Pretty Boy. Add that to his indisputable charisma, and a disturbing amount of fans have turned him into a figure worthy of support and admiration, despite his active attempts to drive all worlds to destruction so he can remake them to his liking, and the thinly-disguised sadistic pleasure he takes in doing it. This might explain why the later books stress those parts.
In The Prayer Warriors, Luke joins the Prayer Warriors much like Draco Malfoy does. Amusingly enough, in The Evil Gods Part 2, Thalia (who, like the rest of the Percy Jackson cast, is out of character), maintains that Luke can't possibly be the traitor they're looking for.
Many Janeites dislike the quiet, shy, timid Fanny Price of Mansfield Park, atypical among Austen's otherwise sassy, witty, Deadpan Snarker heroines. Consequently, many critics are drawn to the Mary Crawford and somehow claim she actually has the personality more typical for Austen's heroines. Because Elizabeth Bennet, Elinor Dashwood, and the rest all considered love secondary to money in marriage, would try to persuade a friend to marry a man she doesn't love, and would callously wish for someone's ill older brother to die so that he would get his inheritance and therefore be rich enough to marry, right?
While it doesn't excuse her actions, some of the love for Mary probably comes from a few kind moments where she comforts Fanny after everyone harasses her.
All of the Feanorians from The Silmarillion sometimes fall prey to this. They do have redeeming qualities, but they're still definitely not complete innocents, what with having slaughtered many innocent people over jewelry:
This is most common with Maedhros and Maglor, who coincidentally happen to be the most sympathetic of a group. But acting as a Parental Substitute for Elrond and Elros and (briefly) contemplating a Heel-Face Turn don't change the fact that they participate in all three of the kinslayings, destroying the kingdom of Doriath and separating Elrond and Elros from their parents to begin with. Then when they are given the opportunity to repent of their murders, they try to steal the Silmarils again. Fan fics tend to portray Maglor in particular as a straight up good guy who was forced to do all these things against his will, if they acknowledge them at all.
Amrod and Amras are just as guilty of murder over the Silmarils as their brothers, but are invariably portrayed as cute Woobies in fandom. At least here it's somewhat mitigated by the fact that one of them wanted to turn back but was killed and the other does practically nothing his entire time in Middle-earth.
Feanor himself is universally lionized despite causing all the conflict in the first place, because, despite being mentally unstable, he is also an omnidisciplinary genius and complete and utter Badass.
Most surprisingly, Celegorm and Curufin have quite a few fangirls despite, unlike their father and brothers, having no redeeming qualities whatsoever.
Caranthir only avoids this because most fans forget all about him.
An in-universe example appears in The Adventures of Tom Sawyer. In the chapter where it's revealed that Injun Joe was dead, it's mentioned that the women of the town had been in the process of getting together a petition to get him pardoned (despite the fact that he committed murder and framed a man too drunk to remember the events of the night properly). As Twain notes, the women would probably have put together the petition if it had been Satan himself being arrested.
Irial from Wicked Lovely. Good looking and interesting, yes, but far from good.
Drake from Gone. In the course of four books, his exploits include: enforcing a brutal semi-police state, forcing a girl to call her autistic brother a retard to his face, leading an effort to encase the hands of several kids in concrete to prevent them from activating powers, holding several children five years or younger hostage, setting coyotes on said children, and torturing the main character while threatening to cause a nuclear meltdown and kill hundreds if the main character doesn't stand and take it. But he still has fangirls nonetheless.
Caine gets this as well, as does Diana. Diana is probably the most understandable, as even she has her limits and is less an outright villain than a morally neutral person in a difficult situation who does what's necessary to ensure her survival, but even she's rather manipulative.
Haruhi Suzumiya: Fujiwara, to some. Probably because he looks like this.◊ It should be pointed out that in canon, Fujiwara has tried to kill at least two minors.
Male fans have been known to do the same to his teammates, though they're Anti Villains and not actually that evil.
In CarpeJugulum, Pratchett deliberately subverts the trope at the end, when the dashingly and deliberately gorgeous male vampire offers a heartfelt plea for salvation from Agnes, the overweight young witch who seems like a personification of so many fangirls, begging her to save him from the angry mob. Agnes, whose qualifications as a Witch of Lancre derive from her exceptional and multifaceted intelligence, contemplates his sexy gorgeousness and the way he fills out those leather pants, then contemplates some of the evil things she's seen, then tells him she'd cheerfully hold their coats while they burnt him to ash and scattered him to the winds.
Even though neither is technically a villain, Edward and Jacob from Twilight could both be considered examples of this. They're emotionally (and sometimes physically) abusive to Bella, they stalk her, and they're scarily possessive of her, and that's really just naming a few things. And yet countless teens (and a disturbing number of grown women) think that these things are actuallyromantic.
Bohun from Sienkiewicz Trilogy ( from "With the Fire and the Sword"). His devotion to Helena is admirable, but lots of the readers forget that Helena feared him due to the fact that his actions were considered violent and unpredictable even by XVII century Cossacks.
The Chathrand Voyages pokes fun at this one. Greysan Fulbreech, introduced in the second and third books, is young and handsome, but slimy and amoral, and his one redeeming feature is that he doesn't have the guts to handle actual evil. He comes off quite negatively, though the real villains are much, much worse. In the fourth book, the history professor who's supposedly putting this story together at some point in the distant future mentions in one of his annotations being accosted by a student member of the "Greysan Fulbreech Self-Improvement Society", who's convinced against all reason that Fulbreech was the real hero of the story and the professor is deliberately slandering him. The professor, who was actually one of the main characters sent forward in time and knew what a louse the real Fulbreech was firsthand, is torn between amusement, exasperation, and disgust.
Takes place in-universe in Jane Austen's unfinished novel "Sanditon":
With a perversity of judgement, which must be attributed to his not having by Nature a very strong head, the Graces, the Spirit, the Sagacity, and the Perseverance, of the Villain of the Story outweighed all his absurdities and all his Atrocities with Sir Edward. With him, such Conduct was Genius, Fire and Feeling. It interested and inflamed him; and he was always more anxious for its Success and mourned over its Discomfitures with more Tenderness than could ever have been contemplated by the Authors.
Invoked in-universe in the first Black Company novel. Croaker, the main character and narrator, is the surgeon of the titular mercenary company and also an amateur historian who keeps the Company's annals. The Company works for an enigmatic female Evil Overlord called the Lady, and Croaker before long starts writing what amounts to bad self-insert Real Person Fic starring himself becoming romantically involved with a romantically idealized version of her. Then Croaker meets the real Lady, and she scares the crap out of him, after which he regards the whole thing as an Old Shame (but it doesn't stop the other Company members from constantly ribbing him about his "girlfriend"). Then, in the last book of the initial trilogy, Croaker gets to know the real Lady better as a deeply flawed but human individual- albeit one with godlike levels of magical power- and ends up falling for her anyway. After she gets Brought Down to Normal and joins the Company herself, they're the Official Couple for most of the series..
The picture book The True Story Of The Three Little Pigs by Jon Scieszka reinteprets the so called "Big Bad Wolf" as just some unlucky guy with a nasty cold who is just trying to borrow a cup of flour from the the Three Little Pigs, who have been given the Ron the Death Eater treatment and are portrayed as highly inconsiderate assholes.