This is the theme of:

Emporer Palpatine ("The Emperor")

Description: Emperor Palpatine is the ultimate villain of the Star Wars saga. This theme represents the pure darkness of his soul. It is usually played by bassoons and other low woodwinds, but most importantly, by the bass section of a choir. This adds a very hollow, devilish feel. This theme returned in Episodes I, II, and III.

This theme was first introduced in Star Wars, Episode VI: Return of the Jedi