Robert Pierce Knowles I (February 25, 1916 – November 3, 1985) was an American businessman and Republican politician. He served 22 years in the Wisconsin State Senate (1955–1977), representing several counties in western Wisconsin. He was the younger brother of Wisconsin Governor Warren P. Knowles (1965–1971).

Born in River Falls, Wisconsin, Knowles served in the United States Army Air Forces during World War II. He then graduated from the University of Wisconsin–River Falls. He was in the insurance and real estate business. Knowles served in the Wisconsin State Senate from 1955 until 1975; his older brother was Warren P. Knowles, the 37th Governor of Wisconsin.^[1][2] Knowles was defeated for re election in 1976 by Democrat Michele Radosevich 52%-48%.