Vacant

Vacants are a race of alien cuckoos that are dumped on planets and start life as humanoid-shaped blobs. Instinct drives them to take what they need from the dominant species. They start with eyes and move on to shape their features before taking personalities to fill the vacant gaps by making eye contact and putting their victims to sleep while they take what they need. Usually they blend in with the aspirations of Mr or Mrs Average, although physically they are often quite striking being attracted to things of beauty. (TDL: The Pictures of Emptiness)