One of the things that has made The X-Men one of the most popular franchises in comic and movie history is the story's inherent moral complexity. The diverse array of mutants that form the X-Men, the Brotherhood, the Horsemen, the Morlocks, and more are drawn from many places and many backgrounds, and all of them have reasons for their ideologies. In a world where mutants are sometimes moving toward the cusp of acceptance and at other times being placed in concentration camps by robotic Sentinels, it's not surprising that many of them have changed their opinions on what direction the mutant race should take.

Xavier's school has always stood for acceptance of Homo sapien and Homo superior alike, but even some of his youngest students have worn T-shirts proclaiming that "Magneto was right." Many heroes have become villains — and by the same token, villains have also repented and become heroes. This list will go through the most popular X-Men characters who, in the comics, have changed sides... sometimes more than once.

Here are 13 X-Men Characters Who Went From Good To Evil (And Vice-Versa).

13. Angel/Archangel

Archangel in X-Men: Apocalypse

A fast fall from grace is experienced by Warren Worthington III, a founding member of the X-Men originally known as Angel, in events that are loosely adapted in the movie X-Men: Apocalypse. During the events of the so-called Mutant Massacre, in which a countless number of Morlocks — a hidden community of mutants living in the New York City sewer — are murdered by a group called the Marauders, Angel's wings are mutilated beyond repair. When the damaged wings develop gangrene, they are forcibly amputated. As one of the rare mutants who actually loved his powers, Warren is heartbroken over the loss of his wings.

This leads him right into the clutches of Apocalypse, who takes him in as one of his four horsemen. Apocalypse brainwashes Angel and recreates him as Death, replacing his lost wings with metal ones capable of firing projectiles. Though Angel eventually breaks free from Apocalypse's control, the ancient mutant's touch has left him forever altered, both physically and psychologically. To reflect these changes, he takes on the new codename of Archangel.

12. Mystique

Rebecca Romjin as Mystique in X-Men

One of the most interesting characters in the X-Men movies has been Mystique, who over the course of six movies has evolved from femme fatale to revolutionary leader. As we await news of exactly what shape the next X-Men movie will take, it's hard to predict what will happen to Mystique now that the movies have boldly transformed her from villain to hero.

However, this evolution isn't completely unprecedented. While the comic book Mystique has never taken quite the same heroic course as her cinematic counterpart, she did at one point work for Xavier as his secret agent, with Xavier protecting her from the authorities as long as she completed missions for him without killing anyone. Sometime afterward, Mystique went on to join the X-Men, but she has since fallen back to her old ways.

 11. Gambit

Gambit - X-Men

Probably the most popular X-Man who has yet to join the team in the movies, Gambit  — currently set to appear in his own film sometime in the next few years — was the Wolverine of the 1990s, especially to kids who grew up with X-Men: The Animated Series. When he first joined the X-Men, Gambit's true nature was obscured within a shroud of mystery, his past largely hidden, other than hints of his prior association with the LeBeau Clan Thieves Guild.

It was only after Gambit had established himself as a worthy member of the team that the terrible truth was brought out into the light. Before joining the X-Men, he had worked for Sinister, and Gambit was in fact the one responsible for assembling the Marauders and leading them into the New York City sewers, whereupon the Mutant Massacre occurred. After this revelation, Gambit was cast out of the team. Though he soon returned to the school and redeemed himself, his past actions have never been completely forgotten.

10. Quicksilver and Scarlet Witch

Scarlet Witch Quicksilver and Magneto

These two twins occupy a unique place within the cinema, as the only two crossovers (or potential crossover, in the case of Wanda) between 20th Century Fox's X-Men universe and Marvel's Avengers movies. It's not such a huge surprise, then, that both franchises have each picked their favorite twin out of the two, and stuck with that one: in the case of X-Men, Evan Peters's Quicksilver has been a breakout character, while Scarlet Witch has become a major force within the Marvel Cinematic Universe movies, particularly in Captain America: Civil War.

As the mutant children of Magneto, the comic book versions of the twins first appear as members of his Brotherhood. Their villainous careers are short lived, as both of them soon reform and become members of the Avengers. Both go on to become integral members of the famous superhero team, though Scarlet Witch is at one point overtaken by a mysterious cosmic entity that pits her against both the Avengers and the X-men, and it results in her depowering most of the mutant population.

9. Polaris

Polaris - X-Men

Quicksilver and Scarlet Witch aren't Magneto's only children. Lorna Dane, better known as Polaris, is not only Magneto's daughter, but also possesses similar magnetic powers. First introduced as a villain, albeit one manipulated by the mutant hypnotist known as Mesmero, Polaris soon joins the X-Men and begins a relationship with Cyclops's brother Alex Summers. Though she and Alex attempt to retire from their adventurous lifestyle, Lorna is again mind-controlled, this time by Malice, who forces her to attack the X-Men as the leader of the Marauders.

Though Lorna has fought to be a hero, her many instances of mind control  — and resulting periods of severe mental instability  — have caused her to wildly fluctuate. After the mutant haven known as Genosha is destroyed by Sentinels, Lorna is found alive in the ruins, building a monument to Magneto. At one point, she became a horseman for Apocalypse. Later, Lorna thoughtlessly attacks a nurse who had cared for Alex Summers at some point in the past. Still later, when Alex breaks off their relationship on the day that was supposed to be their wedding day, Lorna tries to kill him. Lorna's story has been tragic from the outset, and it seems unlikely that she'll ever be fully healed from everything she's been through.

8. Colossus

Colossus in Deadpool

Piotr Rasputin is a gentle giant, a kind soul who has been one of the moral centers of the X-Men for many years. It's no wonder that the writers of Deadpool used him as a way to embody the noble values of the X-Men, albeit more humorously than usual for the character. Born on a farm in Siberia, Piotr first discovered his powers when he saved his sister from a runaway tractor, and has always tried to take the honorable path at all times.

But after a brain injury, followed by the tragic loss of his beloved sister to the Legacy Virus — a mutant-killing epidemic that, in the X-Men universe, stood in as an allegory for the AIDS crisis  — Piotr is driven to join Magneto's Acolytes. It's an uneasy fit, as Colossus tries to counterbalance the extremist stance of the Acolytes with the more compassionate approach he has learned from Xavier, and it doesn't take long for Colossus to return to the side of good. Eventually, he goes on to sacrifice his life to end the Legacy Virus, curing everyone who had been infected and stopping its spread.

7. Rogue

Rogue Marvel X-Men

One of the most identifiable X-Men of all time, Rogue actually begins her career as a member of the Brotherhood, a runaway who has been adopted by Mystique. More lost and manipulated than truly villainous, Rogue is ordered by Mystique to sneak up on Carol Danvers, who is at this point operating under the codename Ms. Marvel, in order to absorb her powers of super strength and flight. Rogue attacks Carol, and the prolonged contact between them during the fight results in Rogue permanently absorbing both Carol's powers and many of her personality traits.

Rogue continues for some time as a member of the Brotherhood, until her consciousness becomes increasingly fractured by the psychological pieces of the many people she has absorbed. Unable to control what's happening to her, Rogue flees to Charles Xavier, who helps her come to terms with her powers. Since then, she has been a regular mainstay of the X-Men, her villainous past put fully behind her.

6. Bishop

Bishop - X-Men

While many X-Men have fallen to the dark side, few have fallen as far as Lucas Bishop. A time traveler from a dystopian future, Bishop comes back to the past in order to stop an unknown traitor within the X-Men's ranks from one day destroying the team, an event which will create the terrible future that Bishop hails from. To do this, Bishop joins the X-Men, the team of mutants who he has idolized since he was a young boy, and watches carefully to make sure that this future never occurs.

After a significant portion of the mutant population is depowered by the Scarlet Witch, the future of mutantkind is put at risk, with the very real possibility that no new mutants will ever exist. This all changes when a child is born: Hope, the so-called mutant messiah, the first mutant born since the depowering.

However, it turns out that this child is the one who, in one possible version of events, will kill millions in the so-called Six Second War that creates Bishop's future. Bishop attempts to kill the child, thus unknowingly revealing himself to be the traitor from within the X-Men's ranks that he has sought to stop all this time. Cable, another time traveler from a different future, protects Hope, and this ignites a time-jumping feud in which Bishop fails at killing Hope, but succeeds in killing Cable. Bishop then finds out that in the new future he has created, Cable is memorialized as a hero of mutantkind, while Bishop is forever remembered as the villain.

5. Emma Frost

Emma Frost - X-Men

Formerly the White Queen of the Hellfire Club, a psychic powerhouse who played a role in X-Men: First Class, Emma Frost is known for her cunning manipulations, hardly traits one would normally identify with most heroes. As the White Queen, Emma tortured multiple members of the X-Men, tried to recruit Kitty Pryde into her Massachusetts Academy, and played a role in the Dark Phoenix saga that corrupted Jean Grey.

However, Emma redeemed herself when she and former X-Man Banshee reopened the Massachusetts Academy to create Generation X, a young team of mutants much like the X-Men. After surviving the Sentinel attack on Genosha, Emma finally joins the X-Men, begins a long-lasting relationship with Cyclops, and eventually even becomes co-headmaster of the Xavier school, even taking on an additional role as the school's Ethics teacher —  much to Kitty's understandable irritation. While Emma has never quite become an entirely trustworthy character, she has at this point firmly established herself within the X-Men's ranks.

4. Juggernaut

Juggernaut - X-Men

Charles Xavier's stepbrother Cain Marko has been one of the X-Men's most prominent villains since their 12th issue, but at one point in time, he actually called the X-Men his friends.

When the unstoppable Juggernaut loses the mystical energies granted to him by the Crimson Gem of Cyttorak, leaving him far less powerful than before, he attacks the X-Men with his longtime partner Black Tom Cassidy, but is almost killed in the battle: he only survives when a 10-year-old aquatic mutant named Sammy Paré saves his life. Forming a friendship with the young boy, Marko decides to change the direction of his life. He accepts Xavier's offer to live at the Xavier school, join the X-Men, and reform his old ways.

However, his time as a hero is fraught with problems that are ethical, legal, and psychological in nature, as his enraged temperament and past choices continue to haunt him. After Sammy is killed, Marko's resolve begins to slip, and he eventually embraces the Cyttorak energies once again, returning to his former role as a villain.

3. Cyclops

Cyclops of the X-Men Art

Since the X-Men first began, Scott Summers has been their leader, standing proudly for the values that Xavier taught him since he was a teenager. Cyclops has always been a troubled figure — an outcast who can't properly control his powers, an uptight do-gooder who has often played the foil for Wolverine — but Summers is most recognized for his capacity to lead, and his devotion to Xavier's dream. Cyclops's descent from archetypical hero to questionable antihero is a tragic story of what happens when a man carries the weight of the world on his back.

After Scott and Emma become the new co-headmasters of the school, Cyclops leads the X-Men in a more positive direction, working hard to break down their negative public image and finally make the world see them as the superheroes they are. However, as the persecution of mutants becomes worse than ever before, Cyclops abandons Xavier's dream of unification, instead focusing on the preservation of the mutant race —  by separating them from humanity, stationing them on an island nation named Utopia.

As ruler of Utopia, Cyclops is rallied around as the new face of mutantkind. Even Magneto pledges allegiance to him for uniting all mutants, and while Cyclops becomes an increasingly controversial figure, it isn't until the Schism storyline — where Cyclops begins sending out child soldiers on assassination missions, believing that young mutants need to be soldiers instead of students — that Wolverine splits from him, thereby fracturing the X-Men in two. From this point forward, Cyclops's desperate attempt to preserve the mutant race leads to him taking on the power of the Phoenix, fighting against the Avengers, and finally murdering his adoptive father, Charles Xavier himself —  at which point he is arrested and imprisoned. In the X-Men's world, Cyclops's controversial legacy is now both hated and celebrated amongst mutantkind... much like Magneto, the man who, in the end, he came to resemble far more than Xavier.

2. Magneto

Magneto in X-Men: Days of Future Past

Even as the X-Men's most frequent opposition, Magneto has never been an easy character to place. Both compassionate and unmerciful, Xavier's best friend and worst enemy, Magneto is seen by most of the world as a terrorist, and by others as a mutant revolutionary. His past traumas certainly make him a highly sympathetic character, and while some would claim that he's actually a hero — in the X-Men world, the slogan "Magneto was right" is a popular meme — the vast number of horrific actions he has committed for his questionable goal of mutant supremacy are hardly something to brush aside.

However, in his struggles against the demons within him, Magneto's ideology has fluctuated, and on multiple occasions he has actually come around to Xavier's way of thinking. At one point realizing that his hatred of human beings was just as blind as the Nazi's hatred had been, he accepts Xavier's request for him to take over as the headmaster of Xavier's school under the assumed name of Michael Xavier, posing as Charles's cousin. Though Magneto makes a valiant effort to reform, even going on trial for his past actions, in the end he returns to his prior mission of mutant supremacy. Though Magneto eventually allies himself with Cyclops, this happens only after Summers has begun drifting far away from Xavier's dream of coexistence.

1. Phoenix

Jean Grey as Dark Phoenix in the cover of X-Men

Of course, when it comes  to tales of X-Men gone evil, nothing compares to the Dark Phoenix saga. Largely regarded as one of the most important X-Men stories of all time next to Days of Future Past and God Loves, Man Kills, it's no surprise that the Phoenix Saga was used as the explosive conclusion of the original X-Men trilogy, as well as appearing on multiple X-Men cartoons, in the pages of Ultimate X-Men, and more.

Jean Grey was one of the original X-Men, in many ways the heart of the team, and her death — followed by her rebirth as the Phoenix, a goddess-like entity capable of changing the fate of entire galaxies with a snap of her fingers — should have only been a good thing for Xavier's dream, if her abilities were used for good. Unfortunately, Jean is transformed and corrupted into becoming the Dark Phoenix, using her powers to consume a star, which causes the death of an entire planetary system. Temporarily regaining her sanity, Jean commits suicide in order to save the world and everyone around her.

The Phoenix Saga is one of the most compelling transformations that any comic character has ever made from hero to villain, and while many retellings, retcons, and reboots have been done since, nothing has ever topped the original tale itself. With Phoenix's reemergence in the conclusion of X-Men: Apocalypse, it doesn't seem too unlikely that a new version of this story might be coming in the future, and it will be exciting to see what form it takes.

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Can you think of any other X-Men who have traded sides? Let us know in the comments!