In Comics
Giant-Size X-Men #1 (May, 1975)
New Mutants #25 (March, 1985)
Base
Xavier Institute, Salem Center, Westchester County, New York State
formerly Ruth Aldines mind, Utopia, San Francisco Bay, California; Westcliffe, Colorado; "No-Time"; Moira MacTaggarts Mutant Research Center, Muir Island, off the coast of Scotland; Haifa; Paris, France