Unquiet Dead (spoilers)

The Unquiet Dead can be found in the Bloodless Reach, west of Nyryal. They are not a mindless horde of zombies, but other than that, little is known of them beyond the following:

"The Shayardene horror stories speak of the undying lords of the Bloodless Reach – the worst abominations created by Xaos. Cunning and cruel, the kings of the Dead hunt down any living human who dares enter their realm, toy with them to give them some hope of survival… and then torment them to death and feast on their flesh.

"One of the Nyr stories you’ve read speaks of rash scholars who crept off to the Ward to convince the liches to share the centuries of knowledge they possess. The Archlich Ghaesh himself appeared out of the snows to whisper his dark wisdom to them… and over two years of converse, he persuaded them one by one to cross the Ward to learn to see as he saw. Only one refused, insisting that everything could be learned by talking across the Ward. So Ghaesh patiently continued to whisper to him daily… until the scholar’s hair had grown long enough to blow across the Ward as he leaned in to hear the lich. Instantly Ghaesh seized the hair, pulled him bodily across, and devoured all of the foolish scholars."

Source

Archlich Ghaesh
Very little is known about the lord of the Unquiet Dead, other than that at some point in a future game he will try to get the MC to join him.