Vacant

Vacants were a race of alien cuckoos which were dumped on planets. They started life as humanoid-shaped blobs. Instinct drove them to take what they needed from the dominant species on the planets. They began with eyes and moved on to shape their features before taking personalities to fill the vacant gaps. They did this by making eye contact and then putting their victims to sleep while they took what they needed. Usually they blended in with the aspirations of an average person, although physically they were often quite striking as they were attracted to beauty. (TDL: The Pictures of Emptiness)