Agents of Prophecy
According to LLewellyn, Deathless servants are powerful non-corporeal undead that can be bound into specially prepared bodies. There are only ten known to exist, and they usually serve powerful necromancers. They appear as humanoids wrapped from head to toe in black cloth, with red sparks glowing in their otherwise empty eye-sockets. The bodies underneath the cloth are desiccated, but still deadly strong.
The party has encountered one Deathless Servant, after it had abandoned its body. That particular servant appears to have set free The Alpha.