The X-Men have fought against countless enemies in their time, but who are the best X-Men villains?
Some of them are obvious, with many of the X-Men's arch-foes almost as famous as the heroes themselves. But there's the complication - over the years, and especially in the current Krakoa era, many of the X-Men's greatest villains have gone on to join the team or become their allies.
With that in mind, we're thinking a bit outside the box with a few of our picks as we count down the best of the malicious mutants and villains that have faced down the X-Men over the years.
Here are the top 10 best X-Men villains of all time.
Let's face it: shapeshifting - the ability to physically transform yourself into practically anyone - is just a cool power. If that were all Mystique had going for her, she'd still be a pretty good villain.
Luckily for readers, she actually is a multifaceted character who's played both sides of the good/evil spectrum since her debut in 1978, but is best known as a mutant terrorist who led the iconic Brotherhood of Evil Mutants lineup featuring Avalanche, Pyro, Destiny, and the Blob.
Despite her villainous roots, Mystique has been an X-Man several times - including currently working as an agent of Krakoa.
9. Shadow King
The history of the X-Men is filled with telepaths, starting with Professor X and Jean Grey and continuing on to the likes of Emma Frost, Psylocke, and Cable.
Though all of those characters are (mostly) on the side of good, there's bound to be a flipside to all that psychic energy. And there is: the Shadow King, a villain that exists entirely on the psychic plane and has periodically tormented the X-Men since the '80s (specifically making targets out of Storm and Psylocke).
With the ability to control unwilling bodies, The Shadow King has possessed numerous X-Men characters in the past, and in one instance, all of the fictionally important Muir Island in the aptly titled 'Muir Island Saga.'
After helping out the X-Men during 'Empyre,' the Shadow King has begun to once again show his true villainous colors in New Mutants.
Like several characters on this list, Juggernaut has been both an X-Men team member and an X-Men villain.
But given his powers - superhuman strength and unstoppable momentum given to him by an otherworldly demon named Cyttorak - he certainly shines as a bad guy.
Stepbrother to Charles Xavier, the not-entirely-subtly-named Cain Marko has caused problems for the X-Men since nearly the beginning, first debuting in 1965's X-Men #12.
7. Cassandra Nova
Grant Morrison's New X-Men run of the early-to-mid '00s was, like so many of their comic books, filled with big ideas.
One of the biggest was Cassandra Nova, a new X-Men nemesis with a truly bizarre origin. The very short story is that she's Professor X's twin sister, whom he fought in the womb. Though stillborn, Cassandra Nova was able to psychically recreate her body, and then masterminded the destruction of Genosha and the death of millions of mutants, most assuredly earning her place on this list in sheer numbers on the board alone (though uniqueness certainly counts).
Cassandra Nova appeared again during Joss Whedon and John Cassaday's run on Astonishing X-Men, wreaking havoc with Emma Frost as part of a post-hypnotic suggestion.
6. Hellfire Club
Though intrinsically tied to the X-Men's history, the Hellfire Club could conceivably have plagued any Marvel hero. They're an organization of influential, affluent members of society who act in secret to bend the world to their will.
But what makes them perfectly positioned as X-Men villains is the simple fact that many of their key members have been mutants, starting with longtime Black King Sebastian Shaw. Emma Frost has been a mainstay of the X-Men since Grant Morrison’s run, even spending many years as Cyclops’s paramour, making her one of the team’s de facto leaders.
The Hellfire Club has played a part in many major X-Men stories, notably helping to turn Jean Grey into Dark Phoenix during 'The Dark Phoenix Saga.'
Now, the Hellfire Club has become the Hellfire Corporation, headed up by Emma Frost, Sebastian Shaw, and Kate (don't call her Kitty) Pryde.
5. Mr. Sinister
With pale skin and a diamond on his forehead, Mr. Sinister is undeniably physically distinctive.
Though a relatively recent addition to the X-Men's rogues' gallery, having debuted in 1987, Mr. Sinister has quickly ascended the ranks to one of their most frequent and feared foes, as a geneticist fascinated with experimenting on mutants and himself.
Even before making a proper debut, Mr. Sinister made his presence felt in a major way via the 1986 storyline 'Mutant Massacre,' where he deployed his Marauders to wipe out the Morlocks, a group of mutants living underground since they couldn't integrate with humans.
Mr. Sinister has since shown himself to be fascinated with the Summers and Grey families, attempted to kidnap Hope in 'Messiah Complex,' died and came back as a woman, and tried to transform San Francisco's population into replicas of himself.
His mutant DNA database is an integral aspect of Krakoan attempts to resurrect dead mutants, with Sinister himself serving on Krakoa's 'Quiet Council' - though his diabolical genetic experiments continue in secret.
4. Dark Phoenix
'The Dark Phoenix Saga' is one of the most revered X-Men stories in history, and at the center of it is, duh, Dark Phoenix. Specifically, that's the twisted (thanks to Mastermind and the Hellfire Club) version of Phoenix, the incredibly powerful cosmic entity connected to Jean Grey.
In the 1980 story, Dark Phoenix attacked her X-Men teammates, and consumed a star's energy, which had the unfortunate side effect of killing billions of alien life forms. Eventually, Dark Phoenix's 'Jean' side won out, and she sacrificed herself before even more destruction could be caused.
It's since been revealed that it wasn't actually Jean Grey committing the Dark Phoenix's deeds, but that doesn't lessen the impact of the story. In Avengers vs X-Men, however, Cyclops had his own run as the Dark Phoenix (and it was definitely him), when he killed Professor Xavier.
Jean Grey is now alive again, and free of the Phoenix Force - possibly forever.
It can be said that the X-Men's greatest villain might be hate. As mutants, they've continually encountered prejudice from the world at large simply for being different - the central metaphor that's carried X-Men comic books for years.
And that hate is embodied most directly in the Sentinels, massive robots originally introduced in 1965 and programmed to seek and destroy any and all mutants. A symbol of humanity's hatred and fear of mutants, Sentinels have come in many forms over the years, but have remained a persistent threat.
In the bleak future seen in 'Days of Future Past,' Sentinels have evolved further, seen in the form of the nearly indestructible, shape-shifting Nimrod. (Yes, that's his name. It means 'Great Hunter' in its Hebrew roots. Education!). They finally made their big-screen debut in the film of the same name in May 2014.
Commonly known as the 'first mutant,' Apocalypse has an origin story that goes way, way back. Like, all the way back to ancient Egypt.
Apocalypse represents perhaps the greatest threat the X-Men have faced what could be greater than a villain who wants to wipe out all life on Earth and remake it in his own image? He's struck the X-Men and the world at large many times, with one of his most lasting crimes including transforming free-wheeling original X-Man Angel into the metal-winged Archangel, the horseman of Death.
In the still-popular '90s story 'Age of Apocalypse,' readers got a glimpse at what the Marvel Universe would be like if Apocalypse won and Professor Xavier never formed the X-Men turns out, it's a pretty scary place.
In the Krakoa era, Apocalypse came to see the X-Men as allies in the future mutantkind, leading to the 'X of Swords' crossover in which Apocalypse was exiled to the dark world of Amenth, away from the X-Men.
Was there ever any doubt?
Magneto is not only the most famous X-Men villain by far but one of the most complex in comic book history. A Holocaust survivor, Magneto has seen first-hand what hatred and fear of those who are different can cause, and has determined that he won't let it happen.
So in that regard, Magneto really isn't a black-and-white villain like many of the characters on this list. His motivations are understandable; even sympathetic. Of course, doing things like ripping out Wolverine's adamantium skeleton or frequently attacking humanity on a massive scale is… less sympathetic.
Still, Magneto is now a longtime member of the X-Men, and one of the two figurehead leaders of Krakoa alongside his longtime friend and rival Xavier.