R.I.P. to Robert Duvall, one of the greatest actors of his generation, or any other.   From Boo Radley in “To Kill a Mockingbird” to Tom Hagen in “The Godfather” movies to Lt. Col. Bill Kilgore in “Apocalypse Now,” Duvall delivered some of the most iconic performances in the history of American film. But he was most celebrated among western fans for his portrayal of Augustus “Gus” McCrae in 1989’s “Lonesome Dove”—a role that gave one of our signature hats its name: The Gus.