Shapechangers

From Glen Cook Wiki

An enigmatic race of uncertain provenance; they appear to be human most of the time, though their true forms appear to be somewhat monkeyish with long limbs, a tail, large lemur-like eyes, and no ears. Shapechangers have the ability to physically mimic other humanoids. They prefer to hit and run, impersonating someone they�ve gotten to know well, briefly, without killing anyone, but sometimes will kill someone and replace them (although this deception is hard to maintain over time, both due to the difficulty in fooling family and friends of the victim, and due to difficulty in maintaining and aging the appearance). It is generally believed that they cannot survive long in their own form. The touch of silver is poisonous to them. It is possible that they communicate with each other telepathically. When Shapechangers are discovered, most other races will set aside their differences and work to exterminate them.

They are apparently very long-lived, with Garrett encountering healthy individuals who fought in the Cantard fifty years previously. They apparently reproduce with sorcery using a process that involves large brewing vats.