The Celestials are cosmic beings who are essentially Marvel’s space gods, and are therefore ranked among the most powerful forces in the universe. These beings are so powerful that one of their flawed creations, the Exterminators, has the potential to cause the premature death of all things — but the X-Men helped defeat them.
Created by Greg Pak, Marjorie Liu, and David Lapham during their run on X-Treme X-Men, the Exterminators were a Celestial-crafted threat that posed a risk to the entire multiverse when unleashed, and just containing them cost an entire reality. The Exterminators were created by the Celestials when they decided to make an avatar of death in their image. As a race of powerful beings capable of casually absorbing energy and matter, the Exterminators gained the ability to steal the life force of others as well, growing larger whenever they absorbed a living being. Before long, the Exterminators, now counting their numbers in the millions, turned on their creators. The Celestials eventually contained their creations in a separate universe while they built the multiverse, intending for their wayward creations to never threaten the universe again.
Why Did the Exterminators Become a Threat?
The barriers, however, erected to contain the Exterminators weakened, and a host of villainous multiversal variants of Charles Xavier worked together to try and harness the power from their dimension. Despite the best efforts of the multiverse-hopping X-Treme X-Men, the Executioners destroyed that entire reality. Things were made even worse when the Age of Apocalypse version of Nightcrawler attempted to make his way back to his reality, with his efforts resulting in the events of the “Extermination” crossover. Recruiting Dark Beast to tear a hole between dimensions, the ensuing rift produced enough damage to the multiverse to rip open a hole to other dimensions, allowing three of the Exterminators to escape into the multiverse and threaten both Earth-616 and the Age of Apocalypse reality.
The X-Men worked with the Age of Apocalypse heroes as well as the X-Treme X-Men to contend with the threat. Multiple members of the X-Treme X-Men were killed in the ensuing battle, while the ultimate plan to contain the monsters included the Jean Grey of the Age of Apocalypse reality embracing not just the power of the Phoenix but those of the mutant Apocalypse as well. Even with such a massive surge in power, Jean was only able to hold the Exterminators at bay.
How the X-Men Defeated the Exterminators
Realizing that the Exterminators would move to other realities after they destroyed the Age of Apocalypse world, the surviving heroes made the difficult choice of trapping the dangerous beings in the world they had already ravaged. After evacuating many of the remaining heroes, the Age of Apocalypse Nightcrawler sacrificed himself to close the portal, successfully trapping the Exterminators and the enhanced Jean Grey in the demolished reality.
Notably, this didn’t defeat the Exterminators entirely, which means that there is still a chance that they could find a way to escape. If that ever happened, the Celestial creations would once again be a genuine and nigh-unstoppable threat to the multiverse.