Who is Duncan Idaho from Dune and what is their importance?

Duncan Idaho is the ruthless "Sword Master" of House Atreides. He makes the first overtures to the Fremen people of Arrakis, hoping they will join the fight against the hated House Harkonnen. Idaho unsuccessfully attempts to save Turok, a Fremen courier, who is put upon by a band of Harkonnens, and he introduces to Leto Stilgar, chief of the sietch he has visited. Idaho and Halleck communicate secretly using battle code while Idaho is in service to Stilgar. Idaho is later recalled after a failed assassination attempt against Paul Atreides. Evidence was discovered implicating Paul's mother, Jessica, and Idaho is tasked to watch her covertly. Idaho later gets drunk, exposes himself, and is eventually killed.