Lovable Traitor

""Lord Varys, I am growing strangely fond of you. I may kill you yet, but I think I'd feel sad about it.""

- Tyrion Lannister, in A Song of Ice and Fire.

A Trickster who seems to have the element of subtlety only in specific clumps. Sometimes the spiritual cousin of the Punch Clock Villain, sometimes a variation on the Enigmatic Minion or a more amenable Les Collaborateurs.

Merely seeing this guy and having a conversation with him for five minutes already cues the hero he shouldn't be trusted too much. He may even openly work for the bad guys, and say threatening things in a non-directed way. Hey, it's his job, nothing personal. And why shouldn't he enjoy what he does?

Your major safety is he likes being entertained, so sometimes will willingly subvert his bosses if he has his own agenda and help you -- or at least not hinder you. He'll get you into trouble, but he'll assure you afterwards he knew you could deal with it. He'll betray you, but he won't tell your enemies all they really need to know about you.

This is Older Than Print -- the archetypical example is the Prose Eddas depiction (which, for whatever it's worth, diverges markedly from that within the older Poetic Eddas) of the Norse god Loki. Much like the Lovable Traitor, it's a misconception to think of him simply as evil -- although he's not above being The Jester in the most classy way he can.

Compare Reliable Traitor, Wild Card, Heel Face Revolving Door and Double Agent.

Anime and Manga

 * Xellos, fan-favorite and self-proclaimed trickster priest from The Slayers. Always an amiable sort, Xellos will often manage to passively "betray" his allies by oops, allowing them to die horribly, alternately help and hinder our heroes and merrily subvert the status quo to his own amusement and greater purpose - sometimes all in the course of one episode.
 * Of course, as a Mazoku, his greater purpose is nothing less than the complete and total destrucion of the universe and everything in it, himself included. At least, that's the theory...
 * Nagi in Mai-HiME (less so in Mai-Otome, where he is the Big Bad)
 * Kurodou Akabane in GetBackers
 * Hisoka from Hunter X Hunter
 * Ken Murata from Kyou Kara Maou, though he is not a villain.
 * Fujiko Mine from Lupin the Third.
 * Sergeant Major Kululu from Keroro Gunsou. He's technically the superior officer, but since he's so sketchy, no one wants to follow him so he's the intelligence officer.
 * Kabuto from Naruto is so ridiculously untrustworthy that even the villain he swore unending loyalty to claims that there's no telling what he'll pull when he's on his own. He can, and has, betrayed everybody he's ever met at least once with a smile on his face and may be on his way to Big Bad status at the moment.
 * Uchiha Itachi. Even before
 * Ichimaru Gin. He has a blatant case of Chronic Backstabbing Disorder, and even deliberately joined  to backstab him (it looked to be the easiest way to get to him).

Comics

 * The Fixer is often this for the Thunderbolts. He frequently switches sides or abandons his friends to die to save his own skin. He doesn't care about money, power, revenge, altruism, duty or loyalty. He only cares about the challenge of a task, proving he's the smartest one in the room and staying alive. He will help save the world or help conquer it provided he is given an interesting technical challenge to figure out.

Film

 * Valentine in Mirror Mask. But he redeems himself completely.
 * Hoggle the grumpy dwarf in Labyrinth.
 * Inverted by D'Arcy in The Perils of Gwendoline in the Land of the Yik-Yak. Originally the traitor who led to Gwendoline getting captured by Amazons. When he tells Gwendoline he is willing to betray the Queen for her sake, she exclaims in exasperation, "You betray everybody!"
 * Captain Jack Sparrow. In the course of the first Film, he ends up allied with and conspiring against every single character down to and including the monkey.
 * Mac from Indiana Jones and the Kingdom of the Crystal Skull.
 * "Jonesy!!"

Literature

 * The Marquis De Carabas from Neverwhere, by Neil Gaiman. Though, more accurately, is the true mole of the group, and is considerably likable. The Marquis on the other hand can be relied upon when he owes you (or your father) a favor - though he much prefers you to owe him.
 * Speaking of Neil Gaiman: Crowley of Good Omens.
 * Long John Silver (and a great many more of Stevenson's characters) in Treasure Island.
 * Varys and Littlefinger in A Song of Ice and Fire.
 * Rupert of Hentzau, one of the main antagonists in The Prisoner of Zenda, will stab just about anybody - hero or villain, whichever seems most fun - in the back, with an amiable smile on his face. The women of Ruritania have a collective crush on him; even the hero keeps bringing up his positive qualities.
 * Dustfinger, of Inkheart, betrays them about twice in the first book, yet each time, and AFTER, they trust him readily enough
 * Edmund Pevensie from Chronicles of Narnia. Although this might be due to the actor's enjoyable personality and looks, especially in the second movie.
 * Arguably, Krager in David Eddings' The Elenium. He's openly and unrepentently on the side of the bad guys (he's basically The Dragon's sidekick), but he has no real loyalty to them, he just thinks they're going to win. If the heroes capture him, he'll trade information for his life, and it's always good information, so they'll accept the deal the next time they capture him. For a certain kind of reader, who finds the self-righteous slaughter by the main characters a bit tiring, he may be the most sympathetic character in the book - at least he's honest about who he is.

Live Action TV

 * Jayne Cobb from Firefly may have made a deal with the bad guy in the pilot episode and tries to turn Simon and River over to the Feds in "Ariel".
 * Harmony, bimbo cheerleader-turned-vampire-turned-perky-executive-assistant, gets a letter of recommendation from Angel even after she betrays him. To be fair, he was counting on her doing it anyway, and she was a pretty good secretary...
 * Dark Angel's Alec, at least before he becomes a full-on good guy, which is a gradual process.
 * In the Doctor Who story "The Daleks' Master Plan," the Meddling Monk makes a reappearance for a few episodes. (He goes around with the heroes, then helps the Daleks in order to save his own skin. Then when the heroes show their contempt for him, he says something like "I hoped I was convincing enough to fool the Daleks, but I didn't think even you would be fooled. This destroys my faith in humanity, it really does."
 * Amanda from the Highlander TV series has a habit of getting Duncan Mac Leod into various kinds of trouble, but never so bad that it's not pretty likely he'll survive it. She really does love him, in her own twisted way, something she is reluctant to admit even to herself, but which pretty much everybody around them recognizes. Duncan's problem is that it's mutual...

Radio

 * Bart Rathbone from Adventures in Odyssey. Little more than a conniving businessman, not above helping the out-and-out villains at one point, and generally the opposite of everything the show stands for. But... it's just so hard not to love the guy sometimes. (It helps that, in practice, he's generally harmless. And he did turn on the bad guys eventually, albeit for selfish reasons.)

Video Games

 * Some of the members of Organization XIII in the Kingdom Hearts are examples, like Axel and Demyx. Axel epitomizes of this during Chain of Memories.
 * The Turks in Final Fantasy VII.
 * As well as Raijin and Fujin in Final Fantasy VIII.
 * Saint Germain in Castlevania: Curse of Darkness.
 * A character in Devil May Cry 3 named literally The Jester falls in this trope before revealing himself to be.
 * Depending on what you do in Tales of Symphonia, falls within this category.
 * In Tales of Destiny:
 * Saemon Havarian from Baldur's Gate II, as Lampshaded repeatedly by CHARNAME, the supporting cast,, and anyone else who's ever had to deal with him ever. If it hadn't been for the fact that sidequests equal more XP and loot, going along with almost anything he says becomes a major point of Who Would Be Stupid Enough...?.
 * Jill, a Wyvern Rider in the Fire Emblem series, becomes a traitor not once, but three times. First, she leaves Daein to spy on Ike in Path of Radiance, which leads to her altogether abandoning her country and joining the Crimean Army. Then, in Radiant Dawn, she's fighting Crimea on Daein's side. Then, it's possible to make her betray Daein and join Crimea again. Luckily, she's heroic enough (and a spectacular unit to boot) that the audience overlooks her constant flip-flopping.
 * In Path of Radiance, she sets two milestones. If you have her on your active team during the mission where you face her father, and they come in contact with each other, she'll switch sides. She has now become the first, and so far only, character unit to be recruitable by the enemy. The second milestone she sets? If she has a strong enough Support bond with Mist or Lethe, they can re-recruit her back to the party after her Face Heel Turn. So not only is she amazingly conflicted and a good unit, she's damn cute too.
 * Naesala, too. In Path of Radiance, he basically sells Reyson into slavery--with the intention of later freeing him, but the heroes beat him to it. He then later, but insists he's still not a good guy. Come Radiant Dawn, and he has betrayed the Laguz Alliance yet again, once more leading to death threats from Tibarn--but once again, he had a perfectly good reason for his actions; Which, when you think about it, might explain his actions in Path of Radiance as well...
 * Some consider  from World of Warcraft to be one of these.   Besides, it's one of the cooler quest chains in an expansion filled with cool quest chains.
 * When his true intentions are revealed he definetly fits this trope:
 * Zevran from Dragon Age is this Hell-Bent for Leather doused in Fetish Fuel.
 * Kanbei Kuroda in Sengoku Basara suffers from a bad case of Chronic Backstabbing Disorder and inevitably tries to seize power for himself against Ieyasu or Mitsunari. However, he suffers from a worse case of being a Butt Monkey and his determination to be The Starscream despite that makes Ieyasu state that he's impossible to despise.
 * Alex from Golden Sun could count.
 * Tales of Vesperia has . Capped off when, to rescue one party member captured due to betrayal, every human party member present punches him in the gut. Later, it's revealed that said captured party member also punched him after the rescue, so as to not be left out.

Webcomics

 * Veilchen the Smoke Knight from Girl Genius. Even the Jagermonsters are impressed at his professionalism as he leaves them to die in an inescapable pit.

Western Animation

 * Bender from Futurama. Most of the time his "Kill all humans" isn't meant seriously. Although in "A Pharaoh to Remember" he loses the Lovable part and becomes The Quisling (and later, ).
 * Teen Titans' Terra, although Your Mileage May Vary. A lot.