Evil Mindflayer Overlord of Toril
Before the Spellplague, Xeratoth sought to rule all sentient life in the Underdark. The gods were now mortal, and Xeratoth thought this the perfect time to gain power unimaginable. His heightened telekinetic abilities allowed him to rule all civilization down below, without any possibility of rebellion. Ruthless, Controlling, Xeratoth became a puppetmaster, enslaving the Duergar, Drow, Deep Gnomes, and even his fellow Illithid. The individual leaders had no idea they were being controlled. It was a perfectly executed stealth takeover, and Xeratoth would soon be overlord of not only the Underdark, but all of Toril. The armies of the Underdark were growing stronger, and the time was almost right for Xeratoth to release his puppets upon the surface.
Then, the Weave collapsed, causing a cataclysm across all of Toril. The caverns of the Underdark caved in, many great subterranean cities were destroyed, and Xeratoth was imprisoned in a glowing blue crystal of pure magic, imprisoned there for nearly 100 years.
It is not known how he escaped from his tomb, but Xeratoth has returned to Toril, slowly and silently enslaving the armies of the surface world so that he may some day rise again and become the supreme ruler of Toril.