Since their first appearance in X-Men #1 way back in 1963, the Uncanny/Astonishing/X-treme X-Men have taken on many foes. Usually, the people they fight are out-and-out bad guys, or at the very least, anti-heroes with questionable methods: Mister Sinister, Mojo, the Hellfire Club, the Brood, Magneto... the list of folks who want the X-Men dead gets longer every year. But this particular article will not be focusing on the X-Men's official enemies. Rather, we'll be highlighting times the X-Men were forced to face off against one of their own. And unfortunately for the X-Men, for all that they are supposed to be a tight-knit group of outcast heroes, this kind of happens a lot.
So what makes a good X-Man go bad? That depends on the X-Man. Often, there are mitigating circumstances involved, such as hypnosis, brainwashing, extreme stress or vindictive alien entities. But every once in a while, one of the X-Men really is just a bad egg who goes to the dark side of their own free will. This list will cover both kinds of rogue X-Men -- though no, Rogue is not featured here. Now yes, comics being comics, it is very likely that every X-Man to ever exist has turned evil at least once in their career, but we don't have the time or patience to go through that many characters. So instead, here are 20 X-Men who, whether by force or by choice, turned on their teammates, with consequences ranging from mild inconvenience to intergalactic apocalypse.
20 CYCLOPS
Scott Summers was the X-Men's first leader -- besides Professor X, of course -- and one of the team's longest serving and most loyal members. He has even been known to put the team's needs above those of his family. But his tenure has not been without controversy.
Like Jean Grey before him, Cyclops fell victim to the Phoenix Force. In Avengers vs. X-Men, he ruled the world with a few other Phoenix-possessed X-Men. Even after recovering, Cyclops' tactics have continued to rankle. He tried to create a mutant army to defend mutantkind, a plan which many of his teammates and even Cyclops' time-displaced younger self disapproved of.
19 EMMA FROST
Emma Frost, a telepath as powerful as Xavier himself, started out as the villainous White Queen of the Hellfire Club. Over the years, she has occasionally mellowed enough to join forces with the X-Men. But recently, she's been showing signs of returning to her morally questionable roots.
On a visit to Muir Island, multiple X-Men are fatally poisoned by the Terrigen Mist. Cyclops passes away in Emma's arms, and she responds by going off the deep end. Concealing Cyclops' death from the rest of the team, Emma uses her powers to create a fake version of Cyclops. She uses this impostor to start a war between mutants and Inhumans.
18 XORN
Kuan-Yin Xorn has to wear a mask to protect others from his mutation: a miniature star capable of destroying anyone exposed to it. But for a while, he was actually a decent guy. He became a teacher at Xavier's institute, spending most of his time with students with a history of abuse.
If only Xorn's story had ended there. But no, he decided to start using substances. As he fell deeper into addiction, Xorn got the bright idea to disguise himself as Magneto and try to consign all of humanity to concentration camps. Needless to say, the X-Men were not amused, and things didn't go real well for Xorn after that.
17 NIGHTCRAWLER
In Uncanny X-Men #160, readers get to see a particularly nasty potential future for our heroes. On a mission gone wrong, the X-Men get stuck in an alternate dimension whose only inhabitant is the demonic Belasco. elasco, far from rolling out the welcome mat, drops Colossus and Wolverine but spares Nightcrawler, training him in the dark arts.
Over time, this training corrupts Nightcrawler until he is wholly within Belasco's power. We can tell he's evil now because he only wears a loincloth. When the present-day X-Men crash Belasco's dimension to rescue Kitty Pryde and Colossus' sister Illyana, Nightcrawler attacks his younger self without question.
16 ANGEL
X-Men: First Class came out in 2011 and presented a fresh look at the X-Men's origins. Among the team's original recruits is Angel Salvadore, a woman whose wing-like tattoos can become real, functional wings. The future Magneto and Professor X ask her to leave her job at a club to join them, and Angel agrees.
But after witnessing the end of the supposedly indestructible mutant Darwin, Angel ditches the nascent X-Men and joins up with Sebastian Shaw's crew of mutant terrorists. One assumes this didn't work out for her, as she and her rebellious teammates were apparently ended in between First Class and the sequel, Days of Future Past.
15 MYSTIQUE
Once an orphaned mutant child who survived by stealing, Raven found a home with the wealthy Xavier family. She and the Xaviers' son, the telepathic Charles, grew up together as brother and sister. When Charles decided to put together a team of mutants and stop Sebastian Shaw's plot to start a war between America and the USSR, Raven was right there alongside him.
But Charles and Raven's worldviews grew too far apart. While Charles wanted Raven to disguise her obvious mutation as he encouraged peaceful relations between mutants and ordinary humans, the newly dubbed Mystique got sick of hiding. She abandoned Charles' team for Magneto's.
14 STORM
In Uncanny X-Men #146, Doctor Doom turns Storm into a crystal statue. Storm eventually breaks free, but by that point, her claustrophobia has taken over and transformed her into an angry, hyper-powered version of herself. Now calling herself a goddess, Storm shoves her teammates away in order to exact vengeance on Doom. Only the memory of Jean Grey, who also went power-mad not long before, enables Storm to calm down.
This was not the only time Storm betrayed her teammates. On another occasion, Dracula got to her and began the process of turning her into a vampire. In this state, Storm was compelled to attack the X-Men.
13 PROFESSOR X
The Brood, a scorpion-looking alien species, uses unwilling hosts to incubate their young. In Uncanny X-Men #166, the X-Men manage to destroy the Brood embryos inside of themselves, but then they get word that Professor Xavier has also been infected. By the time they rush back to Earth, the Brood queen inside of Xavier has already taken over his mind and is ready to hatch.
After a long fight, Xavier recovers enough to beg the X-Men to kill him while they have the chance. But the X-Men find a better way of resolving things. They ask the space-faring Starjammers to use their advanced medical knowledge to clone Xavier a new body into which they can transplant his brain.
12 MORPH
Morph can shapeshift to resemble anyone. He was a member of the X-Men on the animated series X-Men, which aired from 1992 to 1997. In the two-part episode "Night of the Sentinels," Morph supposedly does not survive an encounter with the titular Sentinels. The X-Men, though saddened by the loss, soon move on.
But Morph lived after all. Alone and confused, he falls under the influence of Mister Sinister, who convinces him that his teammates deliberately abandoned him. A furious Morph infiltrates the team's headquarters to get revenge on his ex-friends, the X-Men. Shapeshifting shenanigans ensue until the team convinces Morph that Sinister lied to him.
11 GAMBIT
In Gambit’s defense, the X-Men ditched him first, having been less than thrilled to find out about his past association with the appropriately named Mister Sinister. Rogue even went so far as to abandon Gambit in Antarctica to slowly pass away. This left him with little choice but to make a deal with a less scrupulous alternate version of himself to keep from becoming a Cajun-cicle.
Now in debt to, uh, himself, Gambit agrees to steal a magical artifact. In the course of performing this task, he runs afoul of the X-Men. So did Gambit turn on the X-Men? Yes, and we all would have done the exact same thing.
10 VULCAN
Gabriel Summers is the artificially aged-up younger brother of the more famous X-Men Cyclops and Havok. Using the codename Vulcan, he joined a back-up X-Men team that Xavier and Moira MacTaggert put together to save the missing original X-Men. The plan ends in disaster when the new X-Men suffer a brutal, horrible defeat on their first mission.
But Vulcan lived after all -- he'd just been dormant for several years. When he finally wakes up, he is plenty angry. The X-Men bear the brunt of his wrath when he ends Banshee and kidnaps Cyclops and Marvel Girl. By this time, Vulcan has grown so powerful that the X-Men are unable to subdue him. Vulcan just leaves and that's that... for a while anyways.
9 MAGIK
As a child, Illyana Rasputin was kidnapped by interdimensional demon Belasco. He held her captive for several years, training her to become a powerful sorceress. Illyana finally returned to the X-Men when she was 13. She seemed normal at first, all things considered, but it soon became apparent that Illyana's lost years had had a greater effect than the X-Men realized.
At first there are only relatively small incidents, like when Illyana loses control and attacks Kitty Pryde in the Danger Room. Later on, things get worse. Illyana takes the name Darkchilde and banishes the X-Men to limbo until Kitty snaps her out of it.
8 WOLVERINE
Given Wolverine's antagonistic personality, it's a little surprising that he hasn't turned on the X-Men more than he has. But for the most part, he restrains himself to verbal sparring and the occasional round of fisticuffs if he disagrees especially hard with a team decision.
And then "Old Man Logan" happens. In an alternate universe, Wolverine believes that he is stopping a swarm of supervillains from invading the X-Men's headquarters. But the "attack" is an illusion cast by the villain Mysterio, who has tricked Wolverine into killing the X-Men. Wolverine is so traumatized by this event that he hares off into the forest for 50 years.
7 BOOM BOOM
X-Men: Evolution aired from 2000 to 2003 and, much like the comics, frequently pitted the X-Men against the Brotherhood of Evil Mutants, although here they are simply called the Brotherhood. For a time, Tabitha Smith, aka Boom Boom, was a member of the former team. She has the ability to create small glowing spheres that explode when thrown.
Her personality proves as explosive as her powers. Boom Boom is just too much of a wildcard to fit in with the other X-Men. She doesn't like Professor Xavier's straight-laced attitude and, deciding that bad guys have more fun, jumps ship to the Brotherhood.
6 POLARIS
Despite being Magneto's daughter and inheriting his magnetic powers, Lorna Dane, aka Polaris, generally shows no interest in following in her father's footsteps. She even joined the X-Men for a time. But of course, she wouldn't be on this list if she hadn't done at least one about-face.
As mentioned elsewhere in this article, Polaris was once brainwashed by Magneto into attacking her ex-teammates. Years later, she did one worse. After Polaris lost her powers during M-Day, she accepted Apocalypse's offer to become Pestilence, one of his Four Horsemen. In this capacity, she tried to create a super-plague to wipe out humanity.
5 HAVOK
Havok, younger brother to Cyclops and powerful mutant in his own right, served with the X-Men for a brief period in the '60s. But he soon decided to retire to the southwest with his girlfriend, Lorna Dane, to pursue his education. Sadly, their villain-free bliss did not last long.
A man calling himself Erik the Red mind controls both Havok and Polaris into attacking the X-Men at an airfield. The resulting destruction, including Cyclops' near demise, seems to bring Havok to his senses. But when he sees Storm knock Lorna out of the sky, it's every Summers brother for himself.
4 JUBILEE
Probably thanks to the influence of the '90s animated series, Jubilation Lee has a reputation for being one of the X-Men's more upbeat members. The fact that her powers involve shooting off pretty lights surely helps. Like many of her teammates, however, she has had her moments of betrayal.
After a bite from Dracula's son, Xarus, Jubilee begins a slow and inevitable transformation into a vampire. Once the metamorphosis is complete, Jubilee turns Wolverine into a vampire as well. Wolvie being Wolvie means he's fine now, and the X-Men lock up poor Jubilee until they can find a cure for vampirism.
3 SABRETOOTH
While Sabretooth has ever been the X-Men's enemy, a couple of people have thought he'd make a decent X-Man himself. Those people were deeply wrong. In X-Factor #123, Sabretooth is fitted with a shock collar that ensures his good behavior. As long as the collar functions, he is a member of X-Factor. But he gradually inures himself to the collar's effects and almost slaughters the team.
Having learned nothing from this episode, the X-Men later push Sabretooth to join their own ranks. This ends in a protracted, dismemberment-filled battle between Sabretooth and Wolverine that the former allegedly does not survive.
2 MAGNETO
Magneto is the X-Men's oldest opponent, having first tussled with them in X-Men #1. Over the years, his characterization has changed considerably, to the point where many people acknowledge that his approach to mutant/human relations has some merits. Now and then, Magneto even attempts a more heroic lifestyle, although this has never stuck.
On one occasion, Magneto agrees to take Charles Xavier's place as both an X-Men and as a mentor to the New Mutants, a younger team of heroes. But it isn't long before Magneto decides that he can serve mutantkind best by being the bad guy, while allowing Xavier and the X-Men to continue their work as the designated good guys.
1 JEAN GREY
In one of the most famous betrayals in comics, Jean Grey fell under the influence of Jason Wyngarde and the Hellfire Club. Over the course of months, Jason’s brainwashing confused and corrupted Jean to the point where she accepted the title of Black Queen and helped him capture her friends.
The Phoenix Force only complicated matters. The combination of brainwashing and newly developed god-like powers proved a nigh-unbeatable one for the X-Men, who couldn't stop her no matter what they tried. Jean, as Dark Phoenix, went on a rampage, destroying an entire planet full of intelligent beings. In the end, Jean regained enough control to end her own life before she could hurt anyone else.