Xhemozax

Xhemozax is an ancient undead Beholder who lives in the underdark, deep below Memodir. He (and his minions) is in a permanent state of conflict with the Nedellim, and the Nedellim view their primary purpose to be to defend against the incursion of Xkemozax's minions.
Xhemozax is a Death Tyrant, a Beholder that has lived so long in such fear of death it has inadvertently passed into undeath, not that this diminishes is fear of dying. Amongst a large number of undead minons, he is worshipped as a god by several thousand Troglodytes, and holds sway over a large number of minor aberrations and monstrosities who inhabit the underdark.