Wraithguard
From Warhammer 40k - Lexicanum
The Wraithguard are Eldar warriors who had allready fallen in battle, but due to a dire emergency or lack of living warriors, their Spirit Stones are removed from the Infinity Circuit and placed in bodies of Wraithbone, to fight again. The Craftworld Iyanden features many of these 'Ghost warriors' due to a Tyranid attack on their world.
