The Wraith are ghostly, violent creatures that the essence of wizards who in life threaded the Path of Darkness and live the Neverside and eventually came together to create the "Wraith Lords". These Wraith Lords were guided by their liege and overlord, Warlock. They travelled to the Dayside leaving chaos in their wake fighting a war against Wizardkind. The Wizards created a magical entity called The Key Of Bones from Warlock's hand which would unlock or lock The Line Of Twilight. Putting a barrier between the Neverside and the Dayside to prevent large magical craetures from venturing through to our world. Although sometimes small creatures make it through.
History
When trapped in the Neverside, Tom Clarke warned Lexi of the indigenous Wraiths. The Thirteenth Floor