As Above - So Below
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.
Many believe he is still alive to this day. Some say he is an explorer of the planes, others… fear he is much worse. Much. Worse.