The Esper Saga
Wraiths are horrid beings that drain life energy from their victims. They appear as pale humanoids with vertical slits along their palms, that they use to suck the life out of their victims. Most of them are bestial and stupid, living as gibbering animals in the wilderness. A few seem to have been elevated to near-human intelligence by Professor Siegg, though, and wear clothes and use tools. These intelligent Wraith often become leaders of small packs, and can be quite a threat to human societies.
Apparently the Wraith are far older than previously expected, and their queens have always had elevated intelligence, long before being discovered by Siegg.