Illithid

Illithids, also known as mind flayers, are a race of horrifically evil creatures that live in the Underdark. Their origin is in the nightmarish Far Realms, but at some point long ago they came through to the Material Plane and created a massive underground empire. During the Illithid War they devastated the nation of Estorium, but were ultimately defeated and have been seen only rarely since then.