Dyrr

The undead drow known only as the Lichdrow of House Agrach Dyrr was the de facto ruler of the house and the power behind Yasraena Dyrr's throne.

In addition to his phenomenal power, the Lichdrow had lived for several milennia, and he was once shown to contemplate his possible ascension to divinity in the future. Thus, before his death, he was most probably the most powerful magic user in all the realms.

History
During the War of the Spider Queen, as the priestesses of Lolth and the matriarchal society which they ruled were weakened and exposed, the Lichdrow visited the Archmage of Menzoberranzan Gromph Baenre to encourage him to join in revolution, overthrowing the priestesses to turn Menzoberranzan into some kind of (possibly patriarchal) magocracy. Gromph Baenre refused, and the two most powerful wizards of Menzoberranzan were left on opposing sides. Several lengthy spell battles ensued, in which Gromph Baenre was eventually victorious. Due to the Lichdrow's ability to regenerate at his phylactery, however, he remained undefeated. Gromph Baenre infiltrated House Agrach Dyrr and destroyed the lichdrow's phylactery (which was cunningly hidden in House Agrach Dyrr's temple's guardian golem and protected by many powerful defenses). As a last revenge, the lichdrow had weaved the master ward of House Agrach Dyrr such that if his phylactery was destroyed, an explosion of gigantic proportions would ensue, while a dimensional lock prevented magical escape (and physical escape would be made impossible due to the distance that would have to be covered in the short time between activation of the ward and explosion). Gromph Baenre escaped due to a contingency spell he had placed upon his person prior to his infiltration of House Agrach Dyrr, leaving the Lichdrow finally and comprehensively destroyed.