Sixth Ranger Traitor

""Already there used to be six of you and now there are just five. Pretty soon, Jake, it'll be four.""

-, the Sixth Ranger Traitor of Animorphs

You're a Power Trio or Five-Man Band who just got themselves a new Sixth Ranger. Things are looking pretty good right now -- your team is expanding, you're making new friends. Looks like things might change permanently!

Wait, changing the status quo? Hrm. We'll have to do something about that.

Surprise! It turns out your fancy new Sixth Ranger is evil! He now knows all of your secrets, how to exploit them, and how to push all of your emotional buttons. You've got a new enemy, and the best part is -- you'll have an excuse to keep your team down to a Power Trio or Five-Man Band from now on, so the status quo will remain unchanged.

Just fair warning, this is a trope about betrayal. The names mentioned below may spoil the emotional drama their moment of betrayal brings. However, since Sixth Ranger Traitors tend not to stay with their adoptive teams for long, that may not exactly be much.

Like the Sixth Ranger, The Sixth Ranger Traitor is its own villainous counterpart in a Five-Bad Band, instead reflecting the member of the group who betrays the others, either by pulling a Heel Face Turn, or simply for their own ends.

The name is derived from Sixth Ranger. Sub-Trope of The Mole.

Anime & Manga

 * Kaworu from Neon Genesis Evangelion, although there's enough visual and in-plots hints about people wondering about him that he was deliberately a mysterious character. His character showed up in one episode, which means the time from Introduction to The Reveal about was about fifteen minutes. Subsequent versions of the story are even quicker. Death & Rebirth reveals Kaworu's betrayal before introducing him! The fact that he's first seen in Rebuild of Evangelion hanging out with Keel Lorentz is a pretty big indication by itself that he's not on NERV's side in the latest iteration of the story, either.
 * Corrector Yui - One of the nearest Yui's friends was the true Chosen One to be the titular Corrector, but I.R. chose Yui because an error later explained she was then infected by Grosser  before being recruited after Inukai told everyone in the group about it, then after she tried to leave the group (cause Yui was better for the Correctors) Grosser takes her and turned her against Yui, it was fixed on the next episode but she didn't return as a Corrector until the next season..
 * In the second season opening of Science Ninja Team Gatchaman, the team gets a new G-2 as a replacement for dead Lancer "Condor Joe" Asakura, much to the others' discomfiture. Surprise! He's a Galactor agent. Double surprise!
 * In Death Note, Light Yagami joins the secret police taskforce in charge of finding and stopping Kira, a brilliant but crazy serial killer who's using an Artifact of Doom to anonymously murder anyone he deems evil, which can reach triple digits on a single day. Unfortunately, Light is Kira.
 * It's played with, mind you, in that L, the leader of the task force, is never in any doubt that Light is Kira - inviting him to join the task force is just a ploy to attempt to prove his guilt.
 * from Ikki Tousen starts like this, manipulating both Rakuyou and Nanyou as a Man Behind the Man.  In the anime, at least. The manga's a bit more involved, but  was never evil.
 * Fushigi Yugi's Chiriko was really a Seiryu Seishi named Amiboshii.
 * Team Trinity in Mobile Suit Gundam 00 season 1.  fills the role in season 2.
 * Chrona from Soul Eater is taken in after turning good, then is manipulated back to Medusa.
 * pretends to become a new ally for the heroes of Pokémon Best Wishes for one short Story Arc, but it was just to lure them into a trap in Nimbasa City.

Comics

 * Topher from Runaways. This was less about not changing the status quo, since the team constantly loses and gains members. Topher's betrayal causes the team to be initially suspicious of Sixth Ranger Victor, especially since they know he's the son of a villain (though they don't know which one for a while) and supposed destined to turn evil. Of course, given that every single fricken one of them is the child of at least one, and in most cases two villains, what do ya expect?
 * It's also implied to have happened on purpose, because knew all along that Topher was a vampire (or at least evil) and brought him to the Hostel so that the rest of the group could end up fighting him to be toughened up.
 * In Grant's Morrison's run on X-Men, where the core team starts out as a Five-Man Band, Xorn (For a while, anyhow.) It's worth noting that change and (perhaps futile) attempts to escape the status quo were major themes in this run. The first to join the original Five-Man Band (not counting the Professor) from the sixties, Mimic, also betrayed the team.
 * Nemesis Kid of the Legion in Legion of Super-Heroes. He joined the Legion to spy on them for the evil Khund Empire (and later became a member of the Legion of Super-Villains).
 * Marvel Star Wars does have regulars added to the cast not infrequently. Most of them work out okay - but Shira Brie, Luke Skywalker's Wing Guard and incipient Love Interest, turns out to have been hand-picked by Darth Vader.
 * In an example that would have made fans of the original series cry,, one of the most popular character of the original Voltron: Defender of the Universe series became this in the 2003-4 Devil's Due Darker and Edgier Continuity Reboot.
 * Shun-Day was this to the Legendaries, acting as The Mole to her creator Skroa. She however become the mask and ends up saving the other Legendaries from him. Danael agreed to let her go as a gratitude, but warned her that the next time they'd meet, it'd be as ennemies.
 * Later subverted during the Anathos Cycle when Tenebris, Darkhell's daughter, joins the team. Her motivations for helping the heroes are selfish, she is known to love her father, and even two of the Legendaries (namely Shimy and Gryf) were expecting her to betray them, to the point Shimy even attempted to murder her once it appeared she was of no more use. Ironically, it turned out she never betrayed the team, even when Bigger Bad Anathos gave her the opportunity to join her after he single-handed defeated the other heroes. After the Cycle, she has become a full-time member of the group.

Fan Fiction

 * In Personality Conflicts, this is Tommy's greatest fear. Also played straight with Drew and Bad Future Tasha, but subverted with Ryan.
 * In 72 Hours, Bo is this to the wrestlers. When he moves to America, he falls in naturally with the sadistic group, but has no interest in slaughtering innocents with the others; he simply can't escape. During a battle with SABRE, he not only joins the enemy (pulling a complete Heel Face Turn in the process) but does so in a way that cripples the enemy attack, saving his new friends' lives.
 * Miyako in Death Note and Kamikaze Kaitou Jeanne fanfic, To Kill a Thief is unknowingly playing for Light's Five-Bad Band.

Films -- Live-Action

 * The Losers -.
 * The Expendables -.
 * Sucker Punch:.
 * Transformers: Dark of the Moon:.
 * X-Men: First Class:
 * Lando Calrissian acts as this at in The Empire Strikes Back but he quickly makes a Heel Face Turn and becomes a regular Sixth Ranger

Literature

 * Dragonlance -.
 * Animorphs -.
 * Also by K. A. Applegate, Senna from Everworld.
 * Star Wars Expanded Universe
 * , though it's fairly obvious before he actually becomes a Sith.
 * Kyp in the Jedi Academy Trilogy.
 * In the Coruscant Nights Trilogy,.
 * In Harry Potter: is actually a Sixth Ranger Traitor for a Five-Bad Band, earning himself a (sudden) special place in the hearts of many readers who had previously hated his guts.
 * In The Hunger Games, is this to the Career Tributes.

Live-Action TV
"Spike: Tell you what I'll do then. I'll head out, find this girl, tell her exactly where all of you are, and then watch as she kills you. Spike: Can't any one of your damn little Scooby club at least try to remember that I hate you all? Just because I can't do the damage myself doesn't stop me from aiming a loose cannon your way. And here I thought the evening'd be dull."
 * Tommy Oliver, the Sixth Ranger Trope Namer started out as an inversion of this trope: he was evil at first, but later pulled a Heel Face Turn.
 * Power Rangers uses this inversion as a popular way to introduce the Sixth Ranger - have them fight against the Rangers before defecting to their side. Ryan/The Titanium Ranger in Lightspeed Rescue, Merrick/the Wolf Ranger in Wild Force...
 * Zhane in In Space actually disguised himself as a "Sixth Psycho Ranger" in order to confuse the Psycho Rangers.
 * The Torchwood episode "Adam" had the eponymous mind-altering alien that acting as the team's most trusted member. The viewers know he's the bad guy all along.
 * Buffy the Vampire Slayer:
 * In season 3, Faith is introduced as a second Slayer and hedonistic Shadow Archetype to Buffy. It takes a few episodes, but a fatal accident sets her on a spiral into a Face Heel Turn. She eventually makes a Heel Face Turn and goes back to being one of Buffy's most important allies, though.
 * Rather amusingly, Spike plays the Sixth Ranger Traitor role in season 4 -- selling out Buffy and the Scoobies to Adam - despite the fact that he makes no bones about being evil and hating the Scoobies the whole time:
 * shocked silence from Xander and Giles*


 * from Law and Order Special Victims Unit eventually ends up killing a rapist cop who was found not guilty at trial. To  credit, said cop had previously tried repeatedly to kill him, and in the end he made no attempt to conceal his crime. Much more fitting to the trope is The Scrappy , who turns out to have masterminded a plot to kill the lawyers and judge in a serial killer's murder trial in order to frame the killer, who he had originally accidentally set free due to screwing up the forensic evidence. He ends up killing the Mauve Shirt CSI tech, and almost ends up killing Stabler.
 * from Primeval. And Christine. And Philip. Basically, if the team (or Nick in series 2, and Abby in series 5) hate somebody, then that person is, guaranteed, to be evil!
 * Rick Murray from Degrassi the Next Generation. Crazy, check. Ready to explode, check. Attacks his friends, check.
 * Jorge del Salto from Carrusel.
 * Oddly enough, the reality show Dance Moms has an example of this, when.
 * NCIS had both, who inserted himself into NCIS as part of a long term scheme to get revenge on Tony for ruining his career years ago, and  , who was an enemy double agent. For a while the team pretty much took it for granted that Ziva was one of these, being a double agent for the Israelis, but she eventually proves her loyalty to the team.

Professional Wrestling

 * CM Punk played the good version of this in WWE's ECW revival, infiltrating the New Breed in order to break them apart from within.

Religion and Mythology

 * Hushai plays the role of The Mole for King David in the story of Absalom's rebellion. The guy even has the balls to lampshade it in front of Absalom.

Web Comics

 * The Crossoverlord:

Video Games

 * This is how  was introduced in Mega Man 7.
 * Mega Man X 4 -
 * Final Fantasy series
 * In Final Fantasy IV, when returning to Baron, you run into Cecil's old friend Chancellor Baigan. He "joins" your party (despite the fact that your party is already full (the game doesn't allow six playable characters to be used at once) and he follows along behind you unlike all the other party members who aren't shown on screen during normal gameplay). He is revealed as a monster in disguise about five seconds later.
 * Final Fantasy X - is a shining example of the trope, since he joins the party briefly before turning out to be an Omnicidal Maniac and Complete Monster. (Or, he would be if he wasn't so Obviously Evil).
 * Final Fantasy XII offers one for both sides: The heroes get, and the villains get.
 * Final Fantasy Tactics gives us Algus/Argath, the guest for about half of Chapter 1. Also Gafgarion, a guest for several battles during Chapter 2.
 * Final Fantasy Tactics A2 gives us Adelle, though she's merely Brainwashed and Crazy.
 * Hades, Axel, and Xigbar, all from the Kingdom Hearts series. Hades starts out as part of the Disney villain coalition, but eventually abandons Maleficent's plan for universal conquest so he can keep taking potshots at Hercules. Judging by the fate of his co-workers, he had the right idea. Axel and Xigbar are both part of the Organization; the former eventually makes a sort-of Heel Face Turn, while the latter turns out to be a serious case of Obfuscating Stupidity.
 * Khunag of Albion joins the party quite literally as the sixth ranger. He has little role for awhile. Then at one point, the player must infiltrate the cult he once belonged to, and he's the only guide available. He 'guides' the player into declaring war on the cult, slaughtering their best warriors and eventually killing the leader, with whom he had a score to settle.
 * In Another Day, the bonus chapter of The World Ends With You,, of all people pulls this on Neku Shuto's team of Tin Pin Slammer-playing heroes.
 * from Baldur's Gate II: Shadows of Amn.
 * Harle in Chrono Cross, twice, betraying Lynx for you because and then betraying you for  after you beat FATE.
 * Aydana Kozlova in Ghost Recon: Shadow Wars is a subversion of this trope.

Western Animation

 * Terra from Teen Titans. In the original comics, she was The Mole working for Deathstroke, but in the cartoon, she underwent a Face Heel Turn. If it wasn't obvious enough that Terra as a Titan wasn't going to last long, the episode following her joining the team has her suspiciously absent save a very brief non-speaking cameo in the end, and the title of the next episode when she actually appears as a member of the team? "Betrayal". And then her next two appearences in which she actually invokes this trope? "Aftershock" (Which is a two part episode).
 * William from Code Lyoko. Although he is not evil, he got cocky to the point where XANA succeeded in taking him over. The surprise factor was actually legitimate, because the build-up was so long.
 * Super Robot Monkey Team Hyperforce Go! provides somewhat of a twist on this with Mandarin, because he was originally introduced as "The Sixth Monkey," but it's explained in the beginning of the episode that he was actually the leader of the Hyperforce before Chiro, but they had to get rid of him because he turned evil.
 * In G.I. Joe: Sigma 6, ends up betraying the team to Cobra.
 * from Transformers Animated, who is later revealed to be Shockwave in disguise.
 * Foxglove from Chip 'n Dale Rescue Rangers helped the Rangers mainly so she could steal the episode's Plot Coupons they found, and give them to the villain/goons she worked for... and also because of an affection for Dale, which lead to her Face Heel Turn back to the Rangers.
 * Also, Desiree D'Allure, Monterey Jack's old crush, does this as well... except unlike Foxglove, she stays evil, and even gets away with it! (Well, not completely.)