Introduced in: X-Men #141 (1980)
In one of many possible futures, an assassination of Senator Robert Kelly, Professor X and Moira Mactaggart by the Brotherhood of Mutants led the government to activate the Sentinel Program. While the Sentinel carried out their duties by either capturing or killing mutants, they realized the only way to eliminate mutants was to take over the world. Thus, the remainder of humanity, including mutants, Inhumans and others, were gathered up and sent to internment camps. The last living X-men devised a plan to send Kate Pryde’s mind back to the past. She would inform the X-men of this future and they would work to prevent the Senator’s assassination. However, this future would remain and continue on as a warning to the X-men and mutant kind.
Some of the residents of this universe have traveled back time and now resides in the Prime Universe. These include Rachel Summers, Nimrod and Ahab.