Arkansas's culture is observable in museums, theaters, novels, television shows, restaurants, and athletic venues across the state. Notable people from the state include politician and educational advocate William Fulbright; former president Bill Clinton, who also served as the 40th and 42nd governor of Arkansas; general Wesley Clark, former NATO Supreme Allied Commander; Walmart founder and magnate Sam Walton; singer-songwriters Johnny Cash, Charlie Rich, Jimmy Driftwood, and Glen Campbell; actor-filmmaker Billy Bob Thornton; poet C. D. Wright; and physicist William L. McMillan, a pioneer in superconductor research.