Cats have always been a part of Tolkien's Middle-earth, from the ones who casually prowl around the Shire to the cats who were owned by a queen of Gondor, which she used to spy on her own people.

Source: https://www.cbr.com/middle-earth-terrorized-giant-cat-lord-of-the-rings/

The Witch-king plays a major role in the films, wounding Frodo at Weathertop in Fellowship of the Ring and leading the assault against Gondor in The Return of the King -- ultimately setting up his final fate, falling during a battle to Éowyn.

Source: https://www.cbr.com/tom-bombadil-witch-king-lord-of-the-rings-theory/

This is likely to be seen in movie could still dedicate itself to his rule in Gondor and his slow downfall into the will of Sauron.

Source: https://screenrant.com/lord-of-the-rings-new-movies-lead-character-aragorn-gandalf/