Harold Theodore Spitznagel (December 7, 1896 – April 26, 1975) was an American architect from South Dakota. Spitznagel was best known for residential and institutional architecture, including the original Mount Rushmore visitor center. His styles included Prairie School, Art Deco, and Moderne architecture. He graduated from the University of Pennsylvania, was posthumously inducted into the South Dakota Hall of Fame, and has been called the "foremost 20th-century architect" of the state of South Dakota.