While they may not be quite as famous as The Avengers and Justice League, the X-Men are still the go to superhero team for many comic book fans, and it's not hard to see why. While the heroic members of the mutant race are undeniably compelling, the fact that they've faced so many incredible bad guys over the years is a big part of what keeps us all going back to their adventures. Their rogues gallery is made up of some of the most powerful beings on Earth (and outer space), and while they're all just as iconic as the various evildoers who Earth's Mightiest Heroes have tackled over the years, many of them have yet to be brought to the big screen by 20th Century Fox. That's something which is hopefully going to change over the next few years, as the X-Men's comic book counterparts do fight more than just disgruntled humans - and Magneto - after all. Regardless, out of the thousands of foes the Children of the Atom have come into contact with since their creation, the fifteen you will find here are the best of the best. Some are more well known than others, while the inclusion of at least a few is sure to surprise you. The common thread here is that they're all truly great creations who have pushed the X-Men to the brink of defeat many, many times...
15. Juggernaut
Despite being a brute, the Juggernaut is a surprisingly complex villain. While the stepbrother of Charles Xavier has done plenty of horrible things over the years, one of his best stints came when he attempted to put his bad guy ways behind him to become a member of the X-Men. Tragically, it was the fact that they refused to trust him which ended up putting him back on the path to being a villain in the Marvel Universe. Whether it's taking on Spider-Man, battling the X-Men, or even serving as a member of the Thunderbolts, Cain Marko's journey has been a fun one to follow, and he's a truly formidable opponent for anyone he comes in contact with. After all, he is unstoppable, though he's also a character who has yet to have one of those story arcs which truly establishes him as one of the greats, hence why Juggernaut doesn't place higher here.