Tylwyth Waff is a fictional character from the Dune universe created by Frank Herbert. He is a Mahai, the leader of the Bene Tleilax, and is a major character in Heretics of Dune.
In Heretics of Dune, Herbert provides this description of Waff:
... he appeared an elfin figure barely a meter and a half tall. Eyes, hair, and skin were shades of gray, all a stage for the oval face with its tiny mouth and line of sharp teeth.
The Tleilaxu sustain their lives indefinitely through the use of gholas. In one of his previous ghola lifetimes, Waff had trained under a renegade mentat. The mentats' capabilities were beyond him, and after absorbing as much skills as he could the mentat was killed. One of the skills he gained from this experience was protection against the Bene Gesserit power of Voice.
In Heretics, Waff successfully replaces High Priest Tuek with a Face Dancer duplicate, but loses control due to the copy's complete assimilation into its new form. Waff decides to ally with the Bene Gesserit after he is convinced by Darwi Odrade that the Bene Gesserit are Zensunni and not powindah, the Tleilaxu term for heretics. He has a replacement ghola growing for him in Bandalong, the capital city of the Tleilaxu homeworld Tleilax.
In Hunters of Dune, it is revealed that the Honored Matres who conquered Tleilax kept several of Waff's gholas alive but in vegetative states. In order to recover the supposedly 'lost' secret to producing melange in axlotl tanks, the Lost Tleilaxu scribe Uxtal is tasked to create new gholas from Waff's genetic material. Uxtal accelerates the process artificially, and of the first batch of eight Waff gholas, seven fail to regain their memories and are viciously killed. The massacre shocks the last ghola into regaining some of Waff's memories, but not enough to recreate the melange process. Later, the Waff ghola escapes the Bene Gesserit attack on Tleilax, finding refuge with the Spacing Guild by offering Guild Navigator Edrik the genetic knowledge for the Guild to create their own, optimized sandworms to produce melange.