A tough little banty rooster of a man with a predilection for red cowboy hats, Martin became an essential tenor harmony singer and guitarist for Bill Monroe's primal band, the Blue Grass Boys. He went on to make classic records with his own band, the Sunny Mountain Boys. Director George Goehl's wonderfully gritty documentary follows Martin not merely on stage but squirrel hunting, ranting against the Grand Ole Opry (which has never installed him as a member), and opening thousand-dollar royalty checks. As a portrait of a working-class country musician, King of Bluegrass: The Life & Times of Jimmy Martin artfully belies the title of one of Martin's finest recordings, ''You Don't Know My Mind.'' EXTRAS A useful discography for a guy who's cut a lotta records, and marvelous outtakes of Martin playing a guitar made out of a Prince Albert tobacco can.