WARNING: This article contains spoilers for Astonishing X-Men #7 by Charles Soule and Phil Noto, in stores now.
Writer Charles Soule's Astonishing X-Men has featured some of the biggest mutant names on the team's roster, from Psylocke and Old Man Logan to Mystique, Rogue and Archangel -- and that's just for starters. The series has been a showcase for a genuinely epic X-Men adventure, with things turning deadly for one X-Man in particular when the Shadow King revealed himself as the main villain of the first arc.
But this was only the beginning. Following those events, Professor X made his triumphant return to the land of living. Now, a new body-possessing threat has emerged in the form of an X-Men villain long believed dead: Proteus.
Act I of the series functioned as a way to bring back Charles Xavier into the fold after being dead for nearly five years. When the Professor was killed by Cyclops in Avengers vs. X-Men, his spirit form was instantly locked in a never-ending battle with the Shadow King on the Astral Plane. To the Professor, the battle felt like it had lasted centuries, and it only reached its endgame once the X-Men got involved.
As Charles attempted to recruit Mystique, Fantomex and Rogue to his side in the Astral Plane, the Shadow King launched an attack on London, in the real world. This attack was a psychic infection, taking hold of anyone it touched. Although it began with Logan, the infection quickly spread out all over London like wildfire. Those infected became a sort of unified hive mind, speaking the words "Set me free" over and over again.
Even once the Shadow King was defeated by the Professor in Astonishing X-Men #6, his infection among the citizens of London persisted. As she attempted to cleanse the psychic disease from the people, Psylocke remarked that the infection was doing something to the people, that there was a palpable and distinct energy to it.
In issue #7 of the series, Charles Xavier, now firmly in possession of Fantomex's body, attempted to dispose of the infection by purging it from every single mind it had affected. He gathered it over the city skyline, a massive green sphere of energy hovering over London. However, this energy detonated, and set something else free -- Proteus, who was seemingly also trapped in the Astral Plane.
Proteus is one of the most powerful and dangerous mutants on the planet. The son of mutant genetics expert Moira MacTaggert, he has the power to warp reality and possess the bodies of others, a creature who constantly hungers for more energy. Proteus was last seen eight years ago in 2010's X-Men: Legacy #233, part of the "Necrosha X" crossover event. In that issue, Proteus attacked the X-Men on Muir Island, and it was there that he was defeated by Magneto. But even though Proteus had been defeated, Magneto warned that Proteus would one day return.
Now, that day has finally come. Proteus has returned to torment the world and, according to Bishop's Endtime Database, his resurgence is the precursor to something called the Mindkiller Apocalypse. Whatever that event actually is, we have a feeling we are about to find out.