William Ware Theiss (; November 20, 1931 – December 15, 1992), also called Bill Theiss, was an American costume designer for television and film. His film credits as costume designer include Spartacus, Harold and Maude, Bound for Glory, Pete's Dragon (uncredited), Who'll Stop the Rain, Butch and Sundance: The Early Days, The Man with One Red Shoe, and Heart Like a Wheel. His television credits include Star Trek and Star Trek: The Next Generation, for which he won an Emmy Award for Best Costume Design.In the course of his career, Theiss was most famous for creating alluring female costuming that censors typically could not credibly forbid, employing what came to be called the "Theiss Titillation Theory": "The sexiness of an outfit is directly proportional to the perceived possibility that a vital piece of it might fall off."