William Roy Mettler, Jr. (born October 15, 1946) is an American former competition swimmer and former world record-holder. Mettler represented the United States at the 1964 Summer Olympics in Tokyo. He swam for the gold medal-winning U.S. team in the qualifying heats of the men's 4×200-meter freestyle relay. Mettler did not receive a medal; he was ineligible under the 1964 swimming rules because he did not swim in the event final.