Tevildo was the "Lord of Cats" in The Tale of Tinúviel. He appeared in the form of a great black cat. He captured Beren during the Quest for the Silmaril, but was defeated by Huan and Lúthien when they forced him to reveal the spell which held the stones of his castle together and which held cats under his evil sway.
Later Tevildo's place in the narrative was replaced by that of the Necromancer, Thû (later renamed Sauron), in the legendarium. Thû (and later Sauron) was the "Lord of Werewolves", in contrast to Tevildo's position as "Lord of Cats"; the cat-versus-dog theme prominent in the Tale of Tinúviel was thus eliminated in later writings.