Double Agent

""I never really was on your side.""

- The Spy, Team Fortress 2

The guy who's both The Mole and the Reverse Mole. He works for both sides and plays them off against each other. Although often shown as a villain, he can also be a likeable rogue who just happens to have flexible loyalties, or who has problems with both sides and enjoys setting them on each other.

Although it's possible to find a Double Agent in a crime drama, usually as an inside man in the Mob, he's more often seen in spy dramas. The Double Agent is often The Chessmaster. Becomes the Double Reverse Quadruple Agent when taken to the extreme.

Anime and Manga

 * Ryouji Kaji of Neon Genesis Evangelion is employed by NERV, SEELE, and the Japanese government to spy on and steal information from one another; NERV knows he's a Double Agent, SEELE suspects, and the National Security Agency is relatively clueless. Eventually, one of the factions gets sick of his backstabbing
 * Sideways, from Transformers Armada, masqueraded as an Autobot, then did a Face Heel Turn and "revealed" he was "really" a Decepticon... only to later betray them as well. Turned out he was trying to escalate the war for his Boss' purposes. He made a return appearance in Cybertron.
 * from Naruto was a double agent for  while pretending to be the   mole in the
 * In Bleach,
 * In Bleach,

Film

 * Pirates of the Caribbean's Captain Jack Sparrow.
 * In the film Edge of Darkness, Jedburgh is a british national and "consultant" for the CIA who serves to clean-up politically damaging messes. Throughout the film, however, a seeming crisis of conscience and a liking for the protagonist makes it hard to pin down just where his loyalties truly lie.
 * Bruce Willis' character in the Western flick Last Man Standing.

Literature

 * Harry Potter: Snape. Snape. Severus Snape. His true allegiance is one of the Big Mysteries of the first six books, and, after frantic Epileptic Trees regarding the sixth book's ending, in the seventh it at last turns out.
 * Taken to truly brain-melting levels in the book and film Where Eagles Dare: although everybodies' loyalties are eventually revealed to have been constant throughout, the loyalties they claim ping-pong back andforth like crazy. Check under Batman Gambit for details.
 * On My Honor: the main character is a Double Agent working as The Mole in one kingdom as well as one of its ruler's most trusted assassins. Then he's assigned to murder the king of his home country, an unpopular new ruler. Obviously this makes things... complicated.
 * In Mara Daughter of the Nile, the title character finds herself going from unimportant slave girl to one of these in a battle for the crown in about a day's time. It takes her most of the book to figure out who's side she's really one. Then, it's revealed that Sahure is one as well.
 * All over the Cold War works of John Le Carre.

Live Action TV

 * Ryan O'Reily in the HBO series Oz, who worked rival gang leaders against each other by frequently pledging loyalty to each of them and suggesting opposing plans of attack in order to get them to murder each other. He's rather a self-interested manipulator, using one faction against another to survive.
 * Piggy in Power Rangers SPD, who was supplying Emperor Gruumm, Broodwing and the Rangers all with the same information, and much too terrified to try crossing any of them.
 * Pick a character from Alias. Any character.
 * Ari in NCIS was like this. He was manipulating all sides for personal reasons.
 * Ironically, the heads of both sides thought Ziva was spying on them. As it happens, both Director Vance and her father were completely wrong, but it allowed them to spend several episodes being a Jerkass to the conflicted Ziva.
 * Sam Axe did this for a while in Burn Notice (TV), though not by choice.
 * Alex Krycek of The X Files is this trope to a T. He's introduced as the Mole, but eventually just works for whatever side gives him the most advantage.

Video Games

 * Revolver Ocelot, of Metal Gear Solid fame, is probably the definition of this. With four entries into the series it's unknown to this day exactly who Ocelot is working for other than himself. The end of each game has him talking with some puppetmaster or another over the phone, making known his double, triple, and quadruple crosses but never quite explaining what they are when all is said and done. To wit, he gives an arguably false name to Big Boss at the end of the third game, is revealed to have been masterminding the entire events of it in the third-and-a-half-th game, is apparently both a Man Behind the Man and double crosser to Liquid Snake in the original Metal Gear Solid (working for the President), and is seen "working for" the same (ex) President in a conspiracy in MGS2 up until the end, where it turns out he was actually working for a completely different conspiracy as well as himself.
 * Gets even more complex in Metal Gear Solid 4 where he's
 * Though amazingly, he did tell Big Boss.
 * Basically, it seems Ocelot worked for
 * Loads of them show up in Metal Gear Solid 3.
 * in Tales of Symphonia: he starts out good, then turns out to be, then he helps out the good guys anyway for his own inscrutable purposes. There's also who is working all three sides at once and depending on game choices will either completely join your side after faking a betrayal or actually betray you, fight against you, and die.
 * Not to mention, who starts out trying to kill you (and already acting as a double agent for two sides), then agrees to an alliance, then betrays you, and then finally decides to help you after all when the double agent act collapses. And then there's
 * Pretty much the entire point of Splinter Cell Double Agent, although the player can ultimately determine just who Sam is ultimately working for.
 * The player character in Far Cry 2.
 * The Spy in Team Fortress 2. His entire play style is based around convincing the enemy that you're one of them before backstabbing them. Described in his trading card as a "double reverse quadruple agent."
 * It still hasn't been confirmed if you can dominate one of your own teammates by healing an enemy spy while he backstabs your team.
 * Now it has. It's possible.
 * Called out by name if a Medic targets an apparent friendly spy when calling "Spy!" Indeed, the game mechanics facilitate this -- if, for example, a RED spy disguises as a BLU spy, the BLU team will see that spy as a BLU spy disguised as a RED team member...maybe even a RED spy.
 * Axel, firstly in Kingdom Hearts II. And especially him in Kingdom Hearts Chain of Memories.
 * In Kingdom Hearts 358 Days Over 2, it's shown that Axel wasn't actually a double agent -- he was a quintuple agent. At one point, he  In the end, of course, Axel's only real loyalty is to himself (though he tends to include his friends in that, whether they like it or not).
 * The roleplaying game Paranoia involves so many conflicting goals that the PCs are basically forced into this. Each of them has some part of the mission that they'd love to sabotage if they can get away with it (by either framing a teammate or just ensuring it stays concealed long enough that it can't be traced back to them), but most of them are otherwise loyal (or at least insufficiently opposed) to Alpha Complex and will try to do their job.
 * Harley Filben of Deus Ex works for the NSF as a mole for UNATCO, but is actually working for the NSF as part of his duties for.
 * Star Wars:The Old Republic
 * Imperial Agent story, act 2.

Real Life

 * In one of the greatest intelligence success stories of all time, the British managed to turn literally every German spy in Britain to their service early in WW 2, then used the German intelligence network in England as a massive puppet show to deceive Germany about Allied strength, strategy, and goals.
 * Germany staged a less comprehensive show for the British in turn in Holland and other areas of occupied Europe by seizing resistance cells and their British advisers, making the British waste resources and time.