From Tolkien Gateway
Rankin/Bass was a film production company founded by Jules Bass and Arthur Rankin, Jr. In 1977 Rankin/Bass produced an animated version of J.R.R. Tolkien's The Hobbit. It was followed in 1980 by an animated version of The Return of the King, the final book of Tolkien's Lord of the Rings trilogy. Rankin/Bass could not adapt the first two books of The Lord of the Rings, as the animation rights for the two books were held by Saul Zaentz, producer of Ralph Bakshi's cartoon adaptation of the first half of the trilogy, entitled The Lord of the Rings (1978 film).
The company was dissolved in 2001 and currently, the distribution rights of both The Hobbit and The Return of the King belong to Warner Bros.