Onslaught

Onslaught is a character appearing in American comic books published by Marvel Comics. Created by writers Scott Lobdell and Mark Waid, and artist Andy Kubert, he first appeared in 1996 as a cameo in X-Men: Prime #1 before making his first full appearance in X-Men vol. 2, #53, where he would eventually serve as the main antagonist of the "Onslaught" storyline from then onward. Onslaught was written as a sentient psionic entity created from the subconsciousness of Professor Charles Xavier and Magneto. During a battle between the X-Men and Magneto''''s Acolytes, Xavier used his telepathic powers to shut down Magneto''''s mind, rendering him catatonic. It was explained through the Onslaught crossover series that the darkest aspect of Magneto''''s mind escaped into Xavier''''s subconscious, where it "merged" with Xavier''''s own darker nature to eventually grow into a separate persona of its own.