Mordor is most boldly represented by the theme known alternately as The Evil of the Ring or Sauron's Theme. And that theme is completely associated with one instrument, the rhaita.

Rhaita

The rhaita is an double-reeded, oboe like instrument from North Africa. (Howard Shore refers to it as a Berber instrument and Doug Adams makes one reference to a Moroccan rhaita.) There are many similar types of these double-reed instruments which can be called raita, rhita, ghaita, and ghaita. The sound is loud and spectacular.

USE IN SOUNDTRACK

The rhaita is (almost?) exclusively associated with the Evil of the Ring theme aka Sauron's theme.

ARTIST

Jan Hendrickse played the rhaita in FOTR, TTT, and ROTK.

1. Sample from Joal Fibladijoal, Master Musicians of Jajouka with Bachir Attar, Live Vol. 1

2. Sample from CR-FOTR, Disc 1, Track 7, Keep it Secret, Keep it Safe, 5:53-6:04