By Ben Morse

Every week, a secret cabal of Marvel staffers gathers to discuss the best of the best when it comes to the House of Ideas.

The X-Men have been divided. Unfortunately for the world, their enemies don't seem to care. Evil mutants, bigoted megalomaniacs and killer robots still stalk the Marvel Universe whether the Children of the Atom stand to stop them or not.

This go-around, the Secret Cabal selected their personal picks for the most malevolent menaces to plague the X-Men over the past four decades plus. For each baddie you get a quick bio as well as a special spotlight comic courtesy of Marvel Digital Comics Unlimited.

As always, these picks reflect the personal choices of the Secret Cabal, not the official opinion of Marvel or Marvel.com, and can be considered subjective at best. Enjoy!
10. ONSLAUGHT
First Appearance: X-MEN v2 #53 (1996)
Find Out His Deal… Here
Why He Makes The List: "The very concept of this character hinges on the enduring, enthralling and never boring relationship between Charles Xavier and Magneto. Onslaught is big, ambitious and the kind of threat worthy of an event. It's hard to think of many villains more terrifying, more powerful and more personal than Onslaught—he is Xavier's dream corrupted by the one man who is supposed to validate it. If he can fail, why can't the dream? Now that's drama!" – Secret Cabal member OneManDynasty
Spotlight Comic: ONSLAUGHT: MARVEL UNIVERSE #1—Not content just to bug the X-Men, Onslaught takes on the Avengers, Fantastic Four and more as well, with the heroes paying a horrible price for victory.

9. STRYFE
First Appearance: NEW MUTANTS v1 #87 (1990)
Find Out His Deal… Here
Why He Makes The List: "What makes Stryfe such a great foe for the X-Men isn't his cool powers or rad costume, it's his very personal connection to several of their key members and the fact that so much of his hatred towards them feels quite justified. 'The Chaos Bringer' grew up wanting revenge on his 'parents,' Cyclops and Jean Grey for supposedly abandoning him—only to learn he was but a clone of their real son, Cable. If you learned your whole life was a lie and you couldn't even claim your anger for your own, wouldn't you be ticked too?" – Cabal member Annihilator882
Spotlight Comic: UNCANNY X-MEN #294—Posing as his genetic template, the heroic Cable, Stryfe attempts to assassinate Professor X with a techno-organic virus and sets into motion his elaborate revenge scheme against the X-Men.

8. THE SHADOW KING
First Appearance: X-MEN v1 #117 (1979)
Find Out His Deal… Here
Why He Makes The List: "The very first mutant menace Charles Xavier ever encountered—the Shadow King—was, as Professor X has said more than once, in many ways the reason the X-Men were formed. He has the sheer telepathic power to oppose Xavier himself and crush just about any opponent, but prefers to manipulate his enemies into battling one another by tempting them with their darkest desires and making them his puppets. The Shadow King's fondest dream is to rule over a world engulfed in the flames of hatred—he's one bad dude." – Annihilator882
Spotlight Comic: X-MEN v1 #117—Charles Xavier flashes back to his first encounter with the nefarious Shadow King, and his first realization that evil mutants would oppose his dreams of peace.

7. CASSANDRA NOVA
First Appearance: NEW X-MEN v1 #114 (2001)
Find Out Her Deal… Here
Why She Makes The List: "For her opening act, Professor X's evil twin sister used Sentinels to decimate Genosha and exterminate 16 million living beings, human and mutant alike. To follow that up, she stole her twin's body, telepathically forced Beak to beat Beast into a coma, drove half the Shi'ar Empire insane and psychically tortured both Emma Frost and Kitty Pryde. Cassandra Nova is pure, unrelenting evil given form, with seemingly no rhyme or reason to her actions other than to cause suffering. Also, she's a shriveled little bald lady—spooky." – Annihilator882
Spotlight Comic: NEW X-MEN v1 #126—The final battle against Cassandra Nova, with the life of Professor X and fate of the Shi'ar Empire on the line, comes to an explosive climax.

6. MR. SINISTER
First Appearance: UNCANNY X-MEN #213 (1987)
Find Out His Deal… Here
Why He Makes The List: "Unleashed upon the world by Apocalypse, Sinister's parade of death, destruction and genetic manipulation stems back to the 19th Century when he began tinkering with his own DNA. Over the past 100-plus years his devious deeds have ranged from creating the Marauders—who then slaughtered the Morlocks—to cloning Jean Grey—the clone would go on to spark 'Inferno'—and more. Killed more times than most villains, don't expect Sinister to stay away forever." – Secret Cabal member Agent M
Spotlight Comic: UNCANNY X-MEN #239—After months of plotting, Sinister lines up the final chess pieces in his master plan against the X-Men, manipulating Madelyne Pryor into igniting a demonic invasion of Earth.

5. WILLIAM STRYKER
First Appearance: X-MEN: GOD LOVES, MAN KILLS (1982)
Find Out His Deal… Here
Why He Makes The List: "It's been said that there's nothing more terrifying than the evil within man, and Stryker would certainly be evidence of that notion. William Stryker takes the very real prejudice we all feel from the world around us and distills it into a villain who needs only his hate-filled rhetoric to demonstrate his evil. He can be killed, but what he represents won't die with him. It's a base fear of those things different and unknown that plagues Stryker, fueling him and imbuing the character with a disturbed sense of purpose that makes him terrifyingly familiar." – OneManDynasty
Spotlight Comic: NEW X-MEN v2 #23—Reverend Stryker brings his unholy crusade to the front door of the Xavier Institute, and before the day ends, his actions will have devastating consequences for the young students living there.

4. DARK PHOENIX
First Appearance: X-MEN v1 #1 (1963)
Find Out Her Deal… Here
Why She Makes The List: "While many enemies have hit the X-Men hard and caused them great loss, none have hurt them like Dark Phoenix did. Sure DP's ridiculously powerful combination of telekinesis, telepathy and pyrokinesis left the good guys with their fair share of bruises, but having to find a way to stop their beloved Jean Grey by any means necessary really scarred the X-Men forever. For readers, it was the first time a hero had turned on them and gone so tragically wrong. She may not have surfaced in years, but Dark Phoenix is always a nightmare hanging over the heads of X-Men and X-Fans alike." – Annihilator882
Spotlight Comic: X-MEN v1 #135—After suppressing the evil within for months, Jean Grey loses control of Dark Phoenix, scattering the Hellfire Club and drawing the X-Men into a personal conflict they can't afford to lose.

3. APOCALYPSE
First Appearance: X-FACTOR v1 #5 (1986)
Find Out His Deal… Here
Why He Makes The List: Lemme break it down for ya why 'Pocy rocks so much: One, he has one of the coolest villain names in all of comics. Heck, his real name—En Sabah Nur—sounds totally badass. Two, a blue and gray monster with a giant 'A' belt buckle sounds silly but looks awesome. Three, his credo, 'the strong will survive' may be harsh, but shows he's no cackling madman. He's a monster with some rules. But Apocalypse mostly kicks tuchas because he's turned the X-Men's lives inside-out on numerous occasions. Whether it's enlisting Angel, Sunfire, Gambit, Polaris and Wolverine as members of his Horseman, infecting Cyclops' son Nathan with a techno-organic virus or any of his other jerktastic moves, Apocalypse rules." – Agent M
Spotlight Comic: X-MEN: OMEGA—The "Age of Apocalypse" comes crashing down when Apocalypse and his forces go to war with Magneto and his X-Men with casualties resulting on both sides.

2. THE SENTINELS
First Appearance: X-MEN v1 #14 (1965)
Find Out Their Deal… Here
Why They Make The List: "The Sentinels can't be reasoned with. They can't be convinced, bought off or persuaded. They are cold, unfeeling robots with a single, unshakable objective: to exterminate an entire race of people. The Sentinels don't hunt mutants because they feel prejudice or fight the X-Men because they have ambition, they simply follow their programming and will continue to do so no matter what—and that's a large part of what makes them terrifying. Another scary thing about the Sentinels? You can't get rid of them. No matter how many hundreds of Sentinels the X-Men destroy, somebody will always build more. Unlike so many classic Marvel villains, you can't empathize with or relate to the Sentinels, they're just creepy killer robots who keep on coming. They don't want to listen to your side of the story or gloat about their big plans, they just want to fry you." – Annihilator882
Spotlight Comic: UNCANNY X-MEN #142—Travel to a nightmarish future where the Sentinels have instituted martial law over the United States and only a rag-tag band of freedom fighters including Wolverine and Magneto stand against their absolute rule.

1. MAGNETO
First Appearance: X-MEN v1 #1 (1963)
Find Out His Deal… Here
Why He Makes The List: "The Secret Cabal has never agreed on a number one choice until now, and if there's anyone deserving of such agreement, it's the man who many would call Marvel's greatest villain—even though it's tough at times to call him a 'villain.' A Holocaust survivor, Magneto has been betrayed by the world around him for every conceivable reason, never given a chance to exist without persecution and though it has seemed time and again that Charles Xavier may be the man to show him hope, fate has never smiled on him. There's a compelling tragedy to Magneto that makes him an antagonist, not a villain—he's out to help his people the only way he believes possible. His intentions are noble. His motivations are understandable. But at some point he becomes twisted and his actions are reprehensible, turning this would-be mutant savior into a potential harbinger for doom. The best X-Men stories have been metaphors for the real world plight of those different from the norm and it's no surprise that the best X-Men foe is more real and more understandable than many of us would care to admit." – OneManDynasty
Spotlight Comic: X-MEN v1 #104—Returned to his prime by Erik the Red, Magneto battles the "new" X-Men—including Wolverine, Storm and Colossus—for the very first time.