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Professor Charles Xavier, founder of the X-Men, has devoted his life to his dream of peaceful coexistence between mutants and the rest of humanity. But even this saintly man's subconscious hates “normal” humans who oppress and even try to destroy mutantkind. What if Xavier's dark side took over? Xavier's shadow self first manifested as a malevolent spirit in X-Men vol. 1 #106 (1977), plotted by Bill Mantlo and scripted by Chris Claremont. Xavier's evil side reappeared as a being called the Entity in Mantlo's comics miniseries X-Men and the Micronauts (1984). Both times Xavier's evil self was defeated, ending its independent existence. Years later, Xavier utilized his telepathic powers to shut down arch-rival Magneto's mind, leaving him in a coma. During this psionic contact, the dark side of Magneto's personality fused with the negative aspects of Xavier's own psyche, resulting in the creation of the independent mental entity called Onslaught (which first appeared in X-Men vol. 2 #53, 1996). Eventually, Onslaught took control of Xavier's mind and body, and possessed both Xavier's and Magneto's superpowers. Onslaught captured Franklin Richards, the son of Reed and Susan Richards of the Fantastic Four, in order to utilize the boy's mutant ability to alter reality. Commanding Sentinel robots, Onslaught launched his war on humanity by conquering Manhattan Island. The XMen, Avengers, and Fantastic Four joined forces to stop him, and Thor rescued Xavier, leaving Onslaught as a being of pure psionic energy. The Fantastic Four and Avengers plunged into Onslaught's form, destroying it from within, seemingly at the cost of their lives. However, Franklin Richards actually transported the heroes to an alternate Earth, from which they eventually all returned safely.