In the X-Men universe, few things are as blurry, complicated and fluid as team alliances. Over the decades we had seen characters we love leave the X-Men to join enemy factions like the Brotherhood of Evil Mutants. Similarly, there have been many, often surprising cases of villainous mutants joining the X-Men ranks. It is hard to picture the X-Men without Rogue, but she actually began as a member of the Brotherhood. It is even harder to picture a mutant mercenary like Sabretooth on the team, but he joined as a temporary means to an end. Then you have the unthinkable, like Cyclops who not only left the X-Men, but also started his own team with Magneto and began employing questionable tactics to combat mutant oppression.
The ongoing changing of alliances is an endlessly employed plot device in the X-Men franchise. Occasionally it makes our jaws to drop. Other times, it is just plain annoying. In the X-Men prequel films, for example, the once deadly mutant villain known as Mystique joins the X-Men. Granted, in that story she was on that team while it was being created, but she quickly jumped on board with Magneto’s Brotherhood, making things as they should be. Then, in Apocalypse, she becomes the X-Men’s teacher. Each new X-Men iteration from film to live-action television and animation puts its own spin on who plays for what team. With that said, there are probably more villains who have joined the X-Men and X-Men who have joined the bad guys (or become them) than most fans may know. Here are 10 villains who joined Xavier’s team of merry mutants and 10 X-Men who betrayed the team.
20 JOINED: EMMA FROST
The telepathic Emma Frost appeared in '80s Uncanny X-Men #129 as the X-Men’s newest and most powerful foe. As the Hellfire Club’s White Queen, Frost antagonized the X-Men for years. Eventually, though, she joined Xavier’s team. After surviving a Sentinel attack on the island of Genosha that took out most of the mutant population, she was rescued and recruited by the X-Men.
Beyond joining the X-Men, Emma also became a teacher at the Xavier Institute. Despite this, she continues to be somewhat of a morally ambiguous character who often leads the X-Men astray as much as she helps them. Just ask Cyclops, who she had a psychic affair with when his marriage with Jean was on the rocks. Talk about cold.
19 BETRAYED: PYRO
Pyro’s role in the X-Men films grew considerably in 2003’s X2: X-Men United. He was only briefly seen in the first film where fans were shocked to see him at Xavier’s school. Come X2, John was both becoming increasingly rebellious and, eventually, started identifying with Magneto’s ideologies.
When John abandoned the X-Men and joined Magneto and Mystique as they left Alkali Lake, it was almost unsurprising. This is especially true after his fire showdown with the police at Bobby Drake’s home. In fact, given Pyro’s well-known status as a member of the Brotherhood in the comics, it was difficult to see him actually staying on to become an X-Man in the films.
18 JOINED: MAGNETO
Magneto has a complicated relationship with the X-Men, more than any other villain. There are several instances in the comics where he has worked alongside the X-Men, run the Xavier Institute, and train the X-Men. In the end, he usually returns to his villainous ways but the X-Men films take a different approach.
In the original films, Magneto maintains his comic book villain status. Only in X2 does he appear to join the X-Men for the greater good, yet he later turns on them when presented with the chance to destroy humanity and he even left Charles to his demise. After the original trilogy ends, something changes off-screen that causes Magneto to officially join the X-Men as seen in the future part of Days of Future Past.
17 BETRAYED: DARK PHOENIX
In theory Dark Phoenix could be considered as having abandoned the X-Men in the original "Dark Phoenix Saga," especially when she had a psychic showdown with Xavier. However, she didn’t trade the team in for another and thanks to that retcon, it wasn’t even really Jean. Looking at X-Men: The Last Stand, however, Jean allowed herself to be wished away by Magneto after she ended Xavier.
The moment Jean leaves with Magneto and goes full Dark Phoenix for pretty much the rest of the film is where the movie really starts to tank. Jean joined Magneto’s brotherhood, though her motives are unclear. In league with the likes of Pyro and Juggernaut, Dark Phoenix takes one last stand against her former team before biting the dust.
16 JOINED: AVALANCHE
In X-Men: Evolution, Avalanche, also known as Lance, is a prominent member of Mystique’s Brotherhood. Though angry and angsty, this version of Avalanche also demonstrates increasing heroic inclinations throughout the series. Though he essentially rules the Brotherhood roost, in the season two episode “Joyride,” he goes to Xavier’s institute to join the X-Men.
Initially the X-Men, including Lance’s romantic interest, Kitty Pryde, are skeptical but Xavier believed it can work out. Later, while helping the New Mutants get out of trouble for stealing the X-Jet, Lance concludes that the X-Men are too high maintenance and too many of them, including Cyclops, have already judged him. Season four’s glimpse into the future shows Lance joins S.H.I.E.L.D.’s Freedom Force.
15 BETRAYED: ICEMAN
When we think of Iceman we don’t picture him as a villain, yet there have been notable instances where Bobby had turned his back on the team. The most notable episode in the comics was in Astonishing X-Men Vol 3 #64. In the story, Bobby turned essentially turned evil after being infected by the Death Seed containing Apocalypse’s power. Among other things, he nearly froze the entire planet before eventually returning to the X-Men.
The '90s X-Men animated series provided Bobby with a more permanent departure from the X-Men. As a student of Xavier’s in the past, Bobby frequently found himself locking horns with Professor X. Eventually he quit the team to run away with Lorna Dane, alias Polaris, and pursue a “normal” life.
14 JOINED: STORM
Any fan of the comics who has watched the film adaptations knows that allegiances don’t always remain true to the source material in live-action adaptations. Such was the case with Storm in X-Men: Apocalypse. Early on in the film Ororo was all too easily lured into becoming the first of En Sabah Nur’s four horsemen. It was not only odd to see young Storm introduced as an antagonist, but it was an origin that just didn’t sit right with us.
Fortunately, Storm turned on Apocalypse during the film’s climactic battle. Inspired by seeing her hero, the mutant liberator Mystique, in action, Ororo defected to the X-Men and Xavier’s new team of mutants was complete.
13 BETRAYED: TIME-DISPLACED ANGEL
The original Warren Worthington III has had a whole slew of issues, but the Angel we are looking at is the time-displaced one that was brought to the present in All-New X-Men. Along with the other four original X-Men, young Angel had a lot to deal with when they arrived including a mutant revolution. They also had to deal with learning what their futures hold when most of them meet their older counterparts.
When Angel sees what becomes of himself in the future and he decided to change his fate. Leaving his fellow original X-Men behind, Angel quit Kitty Pryde’s X-Men team to join the adult Cyclops’ revolutionary band of outlaw X-Men. He is later joined by young Beast, Iceman, and Jean Grey.
12 JOINED: ROGUE
It is no shock the Rogue’s loyalty was initially to the Brotherhood of Evil Mutants, after all, she is Mystique’s adopted daughter. When her powers manifested, and she accidentally put a boy in a coma, Rogue turned to the dark side at Mystique’s urging. It wasn’t until later when she permanently absorbed Ms. Marvel’s powers that Rogue sought refuge with the X-Men.
Rogue’s origins as a villain seem like a thing of the past and never even made it to the movies. The 2000s animated series X-Men: Evolution, however, used Rogue’s origins and defection to the X-Men as a main plot point during its first season. In this instance, she leaves the Brotherhood for the welcoming X-Men when she learns that Mystique plans to weaponize her.
11 BETRAYED: BOOM-BOOM
In the comics, Boom-Boom had a bit of a rough entry into the world of the X-Men, but her loyalties never strayed far from side of good and X-Men: Evolution tells a different story. Tabitha first appeared in season two of the series along with several other new students collectively known as the New Mutants. With a troubled past and mischievous nature about her, she struggled with falling into the role of an X-Man.
Eventually she left Xavier’s team to join the Brotherhood where she could cut loose and run the group in Mystique's absence. Unfortunately, upon Mystique’s return, Boom-Boom was ousted. In the final moments of the series finale during season four, we see a future in which Tabitha has rejoined the X-Men.
10 JOINED: JUGGERNAUT
Juggernaut is one of the last villains we would have expected to join the X-Men. Given his extensive and ugly history with his stepbrother, X-Men leader Charles Xavier, it just didn’t seem possible. Yet, in Uncanny X-Men #410-412, this is what happened.
Juggernaut joined the team as part of a plan with Black Tom Cassidy to destroy them from the inside. Things change when Cassidy betrayed him. Juggernaut elected to stay with the X-Men and attempted to reform his evil ways. He did much better at the Xavier Institute than anyone could have expected. He got along with the students and eventually joined Excalibur. His hero stint didn’t last, however, and he returned to his old ways in part because Cyclops destroyed his brother, Xavier.
9 BETRAYED: ESME CUCKOO
Emma Frost’s clones, the Stepford Cuckoos, have been a mainstay among the X-Men since first appearing in Grant Morrison’s New X-Men. Though there were originally five, most only remember the three we have today. Like Emma, those three psychics are morally ambiguous, but remain generally loyal to the X-Men. As for the other two, Esme defected and ended Sophie in the process.
After falling in love with Xorn, Esme joined his Brotherhood. She was responsible for Emma being shot in diamond form and she manipulated the collective Cuckoo hivemind, convincing Sophie to overdose. When Xorn didn’t return Esme’s affection, she turned on him also, but he ended her. During Esme’s last moments, Emma told her how proud she was of her.
8 JOINED: DANGER
It was quite a surprise to learn that after all these years the X-Men’s computer operated training space, the Danger Room, was sentient. Perhaps even more disturbing is the fact the Professor Xavier eventually learned that the entity was self-aware and yet did nothing. Going by the name Danger, the entity turned the training room on the X-Men, created a robotic body for itself, and became one of the toughest adversaries in Joss Whedon’s Astonishing X-Men.
Despite Xavier’s actions and her battles against the X-Men, Danger actually decided to join them. This was in no small part to “her” realization that she would never overcome her programming that prevents her from actually taking out mutants. She has since worked with X-Force and the X-Men: Blue team.
7 BETRAYED: CYCLOPS
Cyclops journey toward abandoning the X-Men was all but certain after he destroyed Professor Xavier in Avengers Vs. X-Men. Developing an intense, Magneto-like, anti-human, pro-mutant view of the world, Cyclops then started up a mutant revolution. Now in league with Magneto, Magik, and Emma Frost, the X-Men’s former leader and golden boy had a new team.
As a revolutionary and antihero, Cyclops essentially began employing terrorism to fight for mutant rights. Eventually he opened the New Xavier School for the Gifted in the old Weapon X facility. He recruited several mutants including the aforementioned time-displaced X-Men sans young Scott. Cyclops would never rejoin the X-Men -- he was one of the first victims of the Inhuman’s Terrigen Mist, passing away due to M-pox.
6 JOINED: SABRETOOTH
As a seemingly soulless mercenary and member of the Brotherhood of Evil Mutants, Sabretooth was one of the last villains we would have expected to join the X-Men. His entry to the team started the same way as it did for many others -- with Xavier seeing hope in him. While incarcerated by Xavier due to his history of crimes, Sabretooth begins helping the X-Men. With the team, he combats the Phalanx and the X-Cutioner. He later turned on them after Wolverine put a claw through his brain.
Sabretooth later found himself seeking sanctuary among the X-Men while being hunted by The Children. Together with the X-Men, he took on The Children. More recently, he has joined another X-Men team headed up by Magneto to protect mutants.
5 BETRAYED: ANGEL SALVADORE
In the soft X-Men reboot film First Class, Charles and Erik recruit the first team of X-Men which included Angel Salvadore. As these new X-Men hung around the CIA choosing codenames, Sebastian Shaw and the Hellfire Club attacked the compound. Shaw offered for the new mutants to join him in his quest for mutant world domination. With really little convincing, Angel joins the Hellfire Club and later battles the X-Men without hesitation.
Angel never rejoined the X-Men and in Days of Future Past Mystique discovers she was terminated by Bolivar Trask. Meanwhile, in the comics, Angel also abandoned the X-Men. In New X-Men, she, along with her children, joined Xorn’s Brotherhood along with Esme Cuckoo and others. Eventually she rebelled against him as well.
4 JOINED: TOAD
One of the X-Men’s oldest foes, Toad first appeared in X-Men #4. He has been a member of numerous Brotherhood incarnations over his long career and even founded his own at one point. Given his extensive history in the X-Men comics, it seems it was only a matter of time before Toad eventually tried to give up his villainous ways and join their ranks.
Toad’s experience as part of the X-Men varies depending on the universe you look at. In Ultimate X-Men, he left the Brotherhood that himself had founded and accepted Cyclops’ offer to be an instructor at the Xavier Institute. In the mainstream universe, Wolverine gives Toad a job as the school’s janitor. Perhaps not surprisingly, he is eventually fired.
3 BETRAYED: XORN
With all the aforementioned talk of Xorn, it's easy to forget he was first an X-Man. A mutant with a star for a brain, Xorn always wore a full head helmet which helped further confuse us all when he turned out to be Magneto but then, later, had actually really been Xorn all along. We think. As it stands, Xorn was an X-Man and teacher of the institute’s “special class.”
While overseeing this class, Xorn begins to indoctrinate the outcast mutants with Magneto-esque teachings. Eventually most of the class become part of his new Brotherhood and leave the X-Men. Xorn is revealed to be Magneto but, later, Magneto, Xavier, and Emma Frost determine it had been Xorn himself who had become the X-Men’s nemesis.
2 JOINED: APOCALYPSE
Apocalypse is pretty much the biggest of the X-Men’s baddest enemies, but things got complicated when he was resurrected as a child in Uncanny X-Force #1. The young Apocalypse had no memories or desire to destroy. Nevertheless, Fantomex shot him in the head. Taking a blood sample, he then cloned Apocalypse and Evan Sabahnur, also known as Kid Apocalypse, was born.
Evan enrolled in the Jean Grey School of Higher Learning where everyone recognizes his resemblance to Apocalypse. Evan has since become and X-Man and has worked with the time-displaced original five, continuously proving he is not the Apocalypse the X-Men knew. Still, Evan’s dark future has been seen by more than one person, including Deathlok.
1 BETRAYED: TIME-DISPLACED JEAN GREY
As Cyclops continued his revolution, Beast tried to stop him by bringing the original X-Men, including Jean Grey, to the present. In the present, Jean’s abilities quickly expanded, and she became more powerful than she would have been at that age. During "Battle of the Atom," the future Brotherhood, including the adult time-displaced Jean, arrives to send the original X-Men back.
Having never returned to the past, future Jean’s powers grew beyond control. She could only contain them with Xorn’s mask. In the future, she formed a new Brotherhood after Alison Blair was taken out. In the present, the hardened Jean psychically battled Emma and the Cuckoos. Young Jean defeated her, and the older Jean later explodes after her powers go nuclear.