Who is Gurney Halleck from Dune and what is their importance?

Gurney Halleck is a fierce warrior, who is loyal to the of House Atreides. He is also a skilled troubadour, and Paul's favorite among his father's men. Gurney is described as an ugly little man, with a jawline marked by a beet-red inkvine scar that ripples when he moves. The scar was infliced upon him by the Harkonnen on Giedi Prime. Halleck amazes Duke Leto with his combination of songs, quotations, and flowery phrases.