Warning: This article contains major spoilers for House of X #5, by Jonathan Hickman, Pepe Larraz, Marte Gracia, VC's Clayton Cowles and Tom Muller, on sale now.
For the X-Men, death has always been another part of life. Even though mutants are supposedly the next evolution of humanity, they've found themselves pushed to the edge of extinction multiple times by anti-mutant forces and reality warpers who have decimated their numbers.
Within their ranks, the X-Men have mourned almost all of their fellow members at one time or another. Cyclops, Wolverine, Jean Grey and several other major X-Men just died in an attack on a Sentinel space station that could've doomed mutantkind in House of X #4.
However, Xavier resurrects all of those characters in House of X #5 with a process that has seismic implications for the X-Men's world.
Using mental copies of mutant minds created and backed up by Cerebro, genetic material collected by Mister Sinister and the specific powers of five young mutants, Xavier has developed a process for reviving mutants on Krakoa. Between his back-ups and the powers of Goldballs, Proteus, Elixir, Tempus and Hope Summers, Xavier can resurrect mutants with their full power sets by artificially growing bodies, aging them to their natural age and restoring their minds as they were at the time of their deaths.
As that process is explained, House of X #5 revisits the previously unexplained scene that kicked off the series, where several mutants burst out of egg-like husks and crawl towards Xavier.
While that scene hinted at this development, the full magnitude of this revelation is only just coming into shape. As Storm states while presenting the newly-reborn Cyclops, Wolverine and the other mutants who died stopping the creation of Nimrod, the X-Men have defeated "their greatest enemy, death."
While plenty of characters have died and come back to life through some fantastic means, this essentially regulates that phenomenon for all of Marvel's mutants. With this process, any mutant who dies in battle or from any other cause could theoretically be resurrected in their prime.
Although this process is first explained and fully seen in this issue, it's almost certainly not the first time it's happened.
Throughout House of X, dead characters like Banshee and Sophie Cuckoo were seen alive with no explanation. Between their returns and Cyclops' largely nonplussed attitude to his own revival in this issue, it seems like this has been going on for at least some time.
However, Polaris, another veteran X-Man, appears to only have a vague understanding of this process, which suggests that it's still relatively new. Goldballs and Tempus, two of the key players in the resurrection process, didn't even debut until 2013, and they weren't alive at the same time as Xavier until the end of 2017, which means that this has likely only been going on for a matter of months, at most, inside the Marvel Universe.
While it's not clear if Xavier designed Cerebro with the express purpose of backing up mutant brains, it seems like he's been using it for that purpose for a considerable amount of time.
Although House of X mentions that Xavier has grand plans to resurrect all 16 million mutants who were killed in Genosha, it also means that every fan-favorite member of the X-Men who's ever died could be brought back to life, if they haven't already.
In the months leading up to House of X, Uncanny X-Men saw dozens of mutant deaths, all of which can be undone through this process. This process could even revive long-dead X-Men like Thunderbird, who famously died on his second mission with the team in the '70s, or Synch, a Generation X trainee who died in 2000, who've both already been mentioned in House of X or Powers of X.
If this process remains a going concern in the X-Men's world, it could theoretically be used to circumvent mutant plagues like M-Pox or the Legacy Virus or keep mutants from aging out of the prime of their lives.
Even if this is only a temporary phenomenon, this "resurrection machine" will probably give Xavier the largest team of X-Men ever, especially considering how many villains joined Krakoa at the end of the issue.
While Xavier is in the process of establishing Krakoa as a nation and reviving every mutant who's ever died, his ultimate goals still remain somewhat nebulous. Regardless of what his real endgame is, it seems like the X-Men founder is doing everything in his power to set up mutants as the dominant species in the Marvel Universe.