As some of the most powerful beings to ever live, the Celestials have caused problems for the entire Marvel Universe but they have a particularly complicated history with the X-Men. The two groups have come into conflict many times, usually because of Apocalypse, who justifies his cruel philosophy of survival of the fittest by saying he is preparing the world for Celestial judgment.

This rivalry came to a head in the crossover event "X-Termination," when the Exterminators, a race of monsters the Celestials had created and then lost control of were unleashed. Three teams of X-Men from across the multiverse banded together and defeated them, proving that Marvel's mutants are capable of anything when they work together in this story by David Lapham, Majorie Liu, Greg Pak, Andre Lima Araujo, Matteo Buffagni, Roberto De la Torre and David Lopez.

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The Exterminators were unleashed when the "Age of Apocalypse" versions of Nightcrawler and Beast attempted to return to their home universe through the Dreaming Celestial. Wolverine was leading the Astonishing X-Men, which at the time consisted of Iceman, Karma, Northstar, and Gambit in pursuit of Nightcrawler, who had betrayed him and X-Force. The X-Men followed them to the Age of Apocalypse and crossed paths with the coincidentally-named X-Terminated, the heroes from that reality featured in the Age of Apocalypse ongoing series. Led by their universe's version of William Stryker, known as Prophet, the X-Terminated consisted mainly of heroic doppelgängers of human X-Men villains including Francesca Trask, Graydon Creed, Zora Risman, and Donald Pierce, along with Jean Grey and Sabretooth, who had lost their powers. The multiverse-traveling X-Treme X-Men, who were led by Dazzler and included Sage and alternate Earth versions of Wolverine, Cyclops, Charles Xavier, Nightcrawler, and Hercules arrived soon after, hoping to fix a tear in reality that Nightcrawler and Beast's actions had exacerbated.

One of the Exterminators moved out throughout the Age of Apocalypse, another went to Earth-616, and another began absorbing power from the dimensional portal. As the monsters caused more and more destruction and more of them began appearing the heroes became increasingly desperate and some began considering sacrificing one world to stop them, but others objected to this. Jean took on the power of Apocalypse to battle the Exterminators directly but Apocalypse's influence eventually began to corrupt her mind. Sage eventually managed to discover how the Exterminators came to be. After creating life the Celestials decided to also create death in the form of the Exterminators but were unable to kill them when they turned against them so instead they created the multiverse and imprisoned them in walls between the different universes. However, superheroes and villains' constant travel between universes weakened the walls, setting the stage for their escape.

As the chaos continues, with multiple members of the X-Treme X-Men falling in battle, the heroes finally resolve to imprison the Exterminators in the Age of Apocalypse, figuring it is best to sacrifice the already hellish world for the sake of the others. After most folks evacuate to the Marvel Universe, Nightcrawler sacrifices himself to close the dimensional portal, redeeming himself for his mistakes.

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"X-Termination" marked the end of both the X-Treme X-Men and Age of Apocalypse series and served as the culmination of several years worth of stories. The "Age of Apocalypse" first returned to prominence after appearing in "The Dark Angel Saga" in Uncanny X-Force, during which Wolverine and the alternate Jean had developed an attraction for one another, as they believed they would fill the holes left by their respective doppelgängers. This again ended in tragedy, given that Jean presumably died along with the rest of the citizens of the Age of Apocalypse after the Exterminators were imprisoned there.

At the end of the event the alternate Wolverine and Cyclops prepared to retrieve Hercules from the underworld, Dazzler created a tribute to her fallen teammates, and Stryker met with Harper Simmons, an ally to the X-Terminated, to toast them. The "Age of Apocalypse" would not return until the 2015 version of "Secret Wars". Although it was hard-won, the X-Men's victory over an enemy that overpowered the Celestials demonstrates how formidable they are.

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