Doppelgangers take on the forms of others, then kill and eat those whose appearance they have stolen, replacing them completely. The brain is said to be their favourite morsel. Doppelgangers infiltrate positions they can use to further their dark and inscrutable agendas, and prefer to take the forms of the highest members of society.
In their natural shape, Doppelgangers look like walking anatomy diagrams: skinless humanoids with muscle and organs plainly visible. They are rarely seen in this shape except in death, however, as they may take the appearance of anyone they have seen, even down to clothes and armour. Not only that, they are able to ape the mannerisms and personality of their targets so well that even family would have difficulty telling them apart.
Doppelgangers are unable to breed. They can be created solely through magical means.
- Warhammer Fantasy RPG 2nd ED -- The WFRP Companion (pg. 115, 122).