Bene Tleilax

The Bene Tleilax or Tleilaxu (/tleɪˈlæksuː/) are an extremely xenophobic and isolationist society in Frank Herbert's science fiction Dune universe. Genetic manipulators who traffic in biological products such as artificial eyes, gholas, and "twisted" Mentats, the Tleilaxu are a major power in the Imperium. The race is ruled by a small council of Tleilaxu Masters, whose genetically-engineered Face Dancer servants have the ability to mimic any human. The Masters themselves possess a bland and diminutive appearance intended to compel other races to underestimate them. In Heretics of Dune (1984) it is revealed that they are a secret totalitarian theocracy ultimately seeking domination of the known universe. Despite their influence, the Bene Tleilax are universally distrusted and inspire disgust because their products, though desirable, push the limits of the moral proscriptions established by the ancient Butlerian Jihad.

Gaius Helen Mohiam and all the Reverend Mothers within her shuddered. Yes, the Tleilaxu did loathsome things.
— Frank Herbert, Dune Messiah (1969)

Read more about Bene Tleilax:  Technologies, Emperor: Battle For Dune