In his score for Return of the Jedi, John Williams introduced a handful of new memorable themes into the Star Wars saga including that for the Ewoks, Jabba the Hutt, and Luke and Leia. But the only one to have significant reverberations across the ensuing prequel trilogy is the Emperor’s theme.
Celebrating Star Wars Themes, Part 3 of 6: Uses of Darth Vader’s Theme, by Mark Richards
See also:
Part 1: The Force Theme — Part 2: Darth Vader’s Theme