The Necrathillian are a group of magic-users that focus on the journey to true death. Unlike worshipers of the Raven Queen though, they see undeath as simply another stage between life and the final rest. The ranks include incredible necromancers, Shamans, and other members of various skill sets.
They were founded by Mortiver, the Quiet, an extra-planar human Dustman, from the city of Sigil. How he came to Zerith, and why he studies here, are his own business, but he has knowledge, and power, to share, which he does. Only members of the Necrathillian know where their headquarters are, though is it said that if you find a river and pay the ferryboat his due, the path to death will appear, and you might reach their halls. Rarely seen, had they not been referenced in texts by Stillwell Inkblazer, the world might not even know the faction even exists.