Ioulaum

Ioulaum was a great archwizard of Netheril, a beloved champion of his people and the inventor of both the mythallar and the flying enclaves of his empire. When Ioulaum abandoned Netheril to escape the “life drain” dweomers of the phaerimm in -339 DR, panic spread at the news of his disappearance, leading to Karsus casting his spell “Karsus’s Avatar.” Since the fall of Netheril, Ioulaum has survived as an elder brain (the central brain of an illithid community) lich.

Ioulaum is believed to have been responsible for the creation of the first alhoon from his illithid students (he used an arcane ritual to fuse the brains of those students into a elder brain that he then took full control of, destroying their individual wills in the process).

The Exursion Into Extinction
In -3145 DR Ioulaum led a major battle known as "The Excursion Into Extinction", bringing thousands of Netherese spellcasters and warriors to mount an attack against the largest concentration of orcs in Netheril's land at the time.

The Mythallar
Ioulaum is most famous for his invention of the mythallar  in -3014 DR. The mythallar dug deep into the raw, unfiltered magic of the weave. The arcanists of Netheril used it to create quasi-magical items - items that were permanent as long as they were within the one mile range of a mythallar.

As the Oracle of Ellyn’taal
Since the fall of Netheril, Ioulaum has survived as an elder brain (the central brain of an illithid community) lich.

Ioulaum is believed to have been responsible for the creation of the first alhoon from his illithid students (he used an arcane ritual to fuse the brains of those students into a elder brain that he than took full control of, destroying their individual wills in the process).

In 329 DR, Ioulaum is apparently slain by a cabal of illithiliches. Ioulaum's last human apprentice, Tabra, witnessed what she believed to be her master's battle with his own students. This was actually a rite concocted by Ioulaum in an attempt to create an undead elder brain that he would then merge his own sentience upon.

In revenge for her master's apparent death, Tabra slaughtered the last few of Ellyn'taal's mind flayers by casting "Ioulaum's Longevity" on herself in the midst of the community. She then destroyed all records of the spell (except her own and those that Ioulaum himself had secretly hidden away) and fled to the surface.

Ioulaum survives today in the form of an undead elder brain. Only Ioulaum's undead servitors and the ghosts of the mind flayers slain by Tabra remain here with him. The few intrepid explorers who have chanced upon the Oracle of Ellyn'taal have gained bits of arcane knowledge dating back to the height of Netheril from their meetings with it. Thus far, no one suspects that this "oracle" was once the legendary Ioulaum, but word of its existence has begun to spread in whispers across the North.

Ioulaum extracts a terrible price for the information he provides - the voluntary, permanent loss of some fraction of the questioner's sanity or the complete knowledge of a powerful spell that Ioulaum does not yet know.