User blog comment:Jacknapier10/Which characters cannot appear in the Marvel Cinematic Universe?/@comment-5350299-20140428113836/@comment-25866432-20140510164637

The studios have rights to the franchises, not just the heroes. So Sony owns the main spiderman villains, including Doc Ock, Norman Osborn, Electro, Rhino..... Fox owns the main Fantastic 4 and X-men villains, including Dr. Doom, Galactus, Sentinels, Bolivar Trask, Magneto....