Royal Eugene Castleton (July 26, 1885 – June 24, 1967) was a relief pitcher for the New York Highlanders and Cincinnati Reds. The first native of the state of Utah and the first Mormon to play in the major leagues, Castleton made his debut with the Highlanders on April 16, 1907, and played his final game with the Reds on May 29, 1910. Castleton's potential as a player was undermined by chronic health problems that ultimately forced him to retire. He is most often remembered for pitching a perfect game while playing for a team in the Ohio–Pennsylvania League.