Illithid Lore

Mind Flayers

During the Archaic Age. There were numerous empires and kingdoms. Amidst these were several smaller city-states. Many of these city-states were at the mercy of greater governments and forced to pay tribute or were otherwise mistreated. 
A group of nine Illithids, humans that have been deformed and mutated from extensive use of abyssal magic. Saw an opportunity to manipulate these city states, and lead them to bring down the great nations of this world. Each Illithid began a secret campaign to gain control of these city-states governments from various means of manipulation. Either with a display of magical power, or by secretly pulling beaurocratic strings behind the scenes.
After the Illithid's political pieces were where they wanted them they began and immediate global invasion. Commanding an massive army. Supported by the Illithid's powerful dark magic. Few strongholds could withstand the onslaught. Their magic was used to corrupt the minds of opposing armies and turn them upon their own homelands. Even resurrecting the bodies of the dead and controlling them as mindless thralls. 
This ability to destroy and bend the minds of their enemies earned these Illithid's the title of Mind Flayers.