Just about every superhero or supervillain has a yin to their yang, so to speak. A polar opposite who helps define who the other person is and often serves as a driving motivation in each of their storylines. Batman has his Joker while Goku has his Vegeta. In terms of X-Men, Professor Xavier has the powerful villain Magneto.
The two mutants, both with their own differing and unique ideologies, have been on opposite sides of the battlefield as opponents and allies. They're both different sides to the same coin and, therefore, are always going to be associated with one another. Yet, only a select few comic stories have delved deeply into this complex relationship between the pair of them.
10 Fatal Attractions - Xavier Puts Magneto Into A Vegetative State
Despite their differences, perhaps in a drive for peace between all mutants, Xavier always tried his best to compromise with Magneto, giving him chance after chance to redeem himself. His perspective changed when Magneto went on a rampage where he murdered thousands of people. Or, in some cases, wounded them severely as he did when he critically injured Wolverine upon forcibly removing the adamantium from his body.
Xavier was tired of giving out chances and reached his breaking point. In a last-ditch effort to end this rampage completely, he wiped Magneto's mind to put him in a vegetative state.
9 Planet X - Bonding While Magneto Was Xorn
Upon discovering a captive in a Chinese government prison, Xavier brings Xorn into the X-Men, and Xorn thanks him by using his healing abilities to heal Xavier. The two bonded from there, making Xorn's betrayal all the more heartbreaking.
As it turns out, Xorn was actually Magneto in disguise the whole time—well, he was until Marvel retconned this moment against Grant Morrison's wishes—and this was all a clever ruse to infiltrate the X-Men. The prison was faked and his healing ability was mimicked using nano-Sentinels. Proving how much he really hated Xavier this whole time, Magneto crippled Xavier all over again.
8 Age Of Apocalypse - Magneto Replaces Xavier
This story really highlights just how important Professor Xavier is in leading and guiding the X-Men, seeing as it all takes place in an alternate universe where Xavier was killed when he was much younger and, therefore, never grew up to create the X-Men.
In highlighting this, the storyline also shows just how even in death, Charles will always be linked to Magneto despite their differences. Just as in this universe, it is a more heroic Erik who forms the X-Men in memory of his late friend, Charles Xavier.
7 Powers Of X - Moira's Memories Bring Them Closer
Powers of X goes out of its way to recontextualize the relationship between Professor X and Magneto as we know it. Upon the revelation that Moira MacTaggert is a mutant with regeneration abilities who retains memories from her past lives, she showed her memories to a young Xavier before he created the X-Men.
By the same sword, Moira also showed her memories to a young Magneto. This establishes that through all of their wars against each other, both men pretty much knew the outcome of every interaction, leading to a secret alliance of sorts.
6 Uncanny X-Men - Magneto Stealing One Of Professor X's Loves
Speaking of Moira, Moira has often been romantically linked to Professor Xavier, but she is by no means his only girlfriend in the history of the comics. Another is Amelia Voght, a mutant who can turn her body into a mist.
The two dated briefly before he founded the X-Men and nursed him out of his depression after he first lost the ability to walk. However, thanks to differing opinions on human-mutant relations, she left him and joined Magneto's Acolytes group, increasing the rift between the two frenemies.
5 Ultimatum - Xavier Sticks His Neck Out For Magneto (And Dies)
Set after the events that killed Magneto's children, Quicksilver and Scarlet Witch, the magnetic mutant is suddenly hellbent on both conquering and destroying the world around him.
Hoping to see the best in his former friend, Xavier reaches out to try to talk some sense into him. His efforts result in him getting his neck snapped by his supposed former friend. In the same breath, Magneto unleashes destruction all across the New York area, resulting in the deaths of countless heroes like Beast and Nightcrawler.
4 Uncanny X-Men #161 - Confronting Hydra Together
While it was in 2017 that Marvel teased Magneto becoming an ally to Hydra, it was back in the '80s for Uncanny X-Men #161. In it, he and Professor X actually team up to take on Hydra head-on.
While working at a psychiatric hospital offshore near Haifa, this is actually how the two met and they discovered each other's abilities upon being attacked by Hydra and Baron Strucker. The two bonded after fighting off Hydra together, but the comic also highlighted how and why they went their separate ways after learning of each other's differing views.
3 Trial of Magneto - Xavier Finally Gets To Him
After Xavier had spent years trying to convince Magneto to atone for his sins and answer for his crimes, he finally does in the Trial of Magneto.
The story sees its title character literally put on a trial where he not only answers for his crimes but finally comprehends all of the damage that he had done up to this point. After a lengthy trial, he cries out that he had become reborn, will try to walk down a righteous path, and even wants to lead Xavier's school in the latter's absence.
2 Onslaught - Putting Their Heads Together
As mentioned earlier, it was in the Fatal Attractions storyline that Professor Xavier felt convinced that the only way to stop Magneto's onslaught - get it? - on the world was to reduce him to a vegetative state. However, in doing so, the darkest parts of Magneto's mind crept its way into Xavier's subconscious, specifically into his own dark parts of his mind.
This merging of the minds, so to speak, literally created a mind of its own called Onslaught. In exploring the Onslaught character, the X-Men franchise further explored Xavier and Magneto's differences, similarities, and their overall relationship through the Onslaught storyline.
1 X-Men + Fantastic Four - Teaming Up To Stop Reed Richards
In this ambitious crossover, while trying to find a cure for his own son's mutation, Reed Richards discovers a mutant cure. This compels both Professor X and Magneto to pay Reed a visit, putting their differences aside knowing that a "cure" that could erase their entire race is bigger than their egos towards each other.
In this interaction, Xavier erases a part of Reed's mind so that he could never remember the formula no matter how hard he tried. Their conversation was both a humble compromise and a cryptic warning to Mr. Fantastic.