Face Dancers are a type of human in Frank Herbert's fictional Dune universe. Face Dancers are a sub species of the Tleilaxu which are near perfect mimics. Their name is derived from their ability to literally change their appearance at will.
Originally a Face Dancer was a profession with the Bene Tleilaxu, individuals trained to mimic others using acting and makeup, enhanced by plastic surgery. However, as time went on, the Bene Tleilaxu began to use genetic manipulation to enhance natural ability, such that Face Dancers could change height, increase and decrease apparent mass, change colouring and texture, and change facial features. This genetic manipulation continued to such an extent that Face Dancers could be considered sub-species of humanity or even another species entirely.
Face Dancers were employed for a number of purposes. Initially there principal use was for entertainment purposes, as entertainers, comedians, impersonators and actors. However, their skills were obviously highly useful as spies, assassins and identity stealers; and they were hired by the Great Houses in their continual political, fianancial and military conflicts.
In time the Face Dancers became genetic eunuchs created by genetic engineering. They became sterile creatures, with full sentience, but no sense of self and with a genetically programmed loyalty to the Tleilaxu masters. They can be explicitly controlled by being forced into an hypnotic state with some predefined sound (often a specific whistling noise).
Over most of the history of the Dune universe only the Bene Gesserit trained were able to detect a face dancer by sight; though others are able to detect a face dancer because they are liable to give away their identity, since they lack the memories of the person they replace.
In Dune Messiah, the second book in the series, the plot is driven by a Tleilaxu plot using face dancers to undermine the Emperor Paul Muad'dib, in the hope the Tleilaxu can take control of the Imperium.
Face dancers also play a role in God Emperor of Dune, as they are often involved in largely ineffective battles with Leto's fish speaker police/army.
At the beginning of Heretics of Dune the Bene Tleilaxu feel ready to take control of the Imperium. The Tleilaxu have achieved their long term plan and developed face dancers who are perfect mimics and believe them to be indetectable to the Bene Gesserit. These face dancers take a mind print of the person they take over and possess all that persons memories, therefore the ordinary human has no real way of detecting a replacement. The Bene Tleilaxu intend to take control of the other powers in the Imperium by replacing their leaders with their face dancers. However, by the end of the novel, the Bene Tleilaxu plan lies in ruin, because there are some fatal flaws in their plan. The Bene Tleilaxu never tested the face dancers over a long time period independent of a masters control. We discover in the novel, that after playing their role too long, the new face dancers come to think of themselves as the person they are printed and forget their Bene Tleilaxu origins. At that point, the face dancer effectively becomes the person he or she is mimicking, and passes beyond the control of the Tleilaxu. Nor indeed are these face dancers indetectable to the Bene Gesserit and so by the end of the novel the Bene Tleilaxu look like they will be forced into an alliance with the Bene Gesserit.