Lords of Creation: Ancients of the Void
The Wraiths are souls that for one reason or another, turned away from the pull of Kereth’s Lantern and have chosen to remain on the material plane. They are incorporeal beings of malevolence and hatred, and though they remember being mortal once, that knowledge over time corrodes into little more than hatred for mortals still able to interact with the world.
Wraiths can possess living creatures who do not have souls, or whose souls are vacant from their bodies (see: dreaming). They then use the body to interact with the world, usually causing mayhem and destruction until the body is killed or destroyed in some way. This only excises the Wraith, which then leaves to find a new host. More often than not, the soul of the mortal passes to the afterlife as its body dies, but sometimes they too become Wraiths, seeking to live the life they lost. Ironically, they also rapidly go insane, and become the same thing they hated to begin with.
Wraiths are almost always quickly found out and destroyed, even if the mortals do not realize why their former friend suddenly has gone made, because a Wraith lives only to cause destruction and chaos. A Wraith that could hide its presence and imitate a mortal would be a frightful foe indeed.
Currently, no one has found a way to excise a Wraith from its body without killing the host.
Kereth hates the shit out of these guys, and is currently working on solutions to the above problem and to the Wraiths in general.