This article is from the rec.arts.sf.movies FAQ, by Evelyn C. Leeper firstname.lastname@example.org with numerous contributions by others.
There was a completely independently produced animation of THE RETURN
OF THE KING by Rankin/Bass who also did an animation of THE HOBBIT.
(Someone notes that Tolkien deplored the fact that the "Lord of the
Rings" is considered a trilogy. That's as may be, but I'm afraid
we're stuck with the terminology.)