Dune Chapterhouse book cover
Futars were a genetic human/feline hybrid created by members of the Bene Tleilax who had gone out into the Scattering, allegedly as a tool for hunting down and destroying Honored Matres during a protracted and vicious war between the two groups. They are first mentioned briefly in Heretics of Dune and then appear prominently in Chapterhouse: Dune.
However, Futars were brought into the known universe by the Honored Matres, who kept the creatures as pets. Though dangerous and harboring only sub-human intelligence they could be controlled through intimidation, sex, and emotional imprinting, typically by their owners or designated handlers.
Some Futars also found their way into urban areas on certain planets, such as Junction, where they struggled to adjust to life free of a Handler's guidance. Sheeana took 4 Futars with her during her escape from Chapterhouse.
When the Honored Matres made the unusual step of capturing the water world Buzzell intact, the Bene Gesserit speculated that it was because the Honored Maters wanted to use it as a home for another slave race they had obtained, one that was an aquatic equivalent to Futars. These "Phibians" appear in the Expanded Dune books.