Ralph Stephens Gerganoff (19 January 1887 – 25 November 1966), born Rashko Stoyanov Gerganov, also frequently referred to as R.S. Gerganoff was an American architect.
 Gerganoff was born in Kereka, a village in Dryanovo Municipality, in Gabrovo Province, in northern central Bulgaria on 19 January 1887 and emigrated to the United States via Boston, Massachusetts on 14 Oct 1905. He graduated from high school at Fredonia State Normal College, Fredonia, New York in 1913 and moved to Michigan shortly thereafter where he studied architecture at the University of Michigan, one of nine architecture graduates in 1917. His classmate Robert B. Frantz (1894 in Waynesboro, Pennsylvania – 1971 in Saginaw, Michigan), who began his career with a similar design aesthetic, formed the firm of Frantz and Spence with James A. Spence Sr. (1899 in Saginaw, Michigan – 1970 in Higgins Lake, Michigan) which prospered in Saginaw from 1925 through 1960,. Classmate Lynn W. Fry (1894–1976) formed the Ann Arbor firm of Fry and Kasurin, and produced some of the University of Michigan architectural drawings held in the collection of the Bentley Historical Library., and a number of notable structures such as the Women's Athletic Building and the First National Bank Building. Classmate Chester G. Henninger designed the 1930 Boca Raton Depot in Florida. Classmate Jingzhai Li, 李敬齋, (who went by the name of Ho Lee) was a prominent architect, university dean, author, and Minister of Land in China.
 Gerganoff worked for several years in Detroit, became a naturalized U.S. citizen on 22 January 1920, then in 1927 opened an office in Ypsilanti, Michigan. In time he was to erect many buildings in Ypsilanti, and nearby Ann Arbor.
 From the late 1920s through the 1950s, Gerganoff was to become the unofficial architect of the city of Ypsilanti and its surrounding townships, designing virtually all the public schools, fire stations, the hospital, and other public buildings, as well as Cleary College, the Washtenaw Country Club, numerous churches, business, factories, union halls, and the Salvation Army headquarters in Ypsilanti.  He also designed many private dwellings, ranging from small Cape Cod cottages to large Eclectic and Tudor styled mansions, and apartment buildings.
 For the Michigan State Normal College (later Eastern Michigan University) located in Ypsilanti, he designed the President's Home, at least six resident halls, the Frederick Alexander Music Building, the 1938 football stadium, laboratory and greenhouse, the Administration Building, the Rackham School for Handicapped Children as well as a Service and a Shop building. Some of these structures have since been razed.
 He was responsible for designing around two dozen service stations in the Ann Arbor and Ypsilanti areas, after heavy use many of them have been demolished and replaced.
 In Ann Arbor, he designed several landmark buildings including the Wolverine Building, the Greek Orthodox Church and the Kingsley Apartments.
 Early in his career Gerganoff developed what could be termed a Low Style Art Deco vocabulary. He frequently employs the stepped pyramid shape of Art Deco as well as the rounded corners of the Moderne. He continued designing in the manner well into the 1950s. Following the end of World War II Gerganoff managed to bring his two nephews Steven and Zach Gerganoff to America from Bulgaria and see them trained as architects. Both were to become part of his architectural practice and probably were responsible for his International Style designs of the 1950s and 60s.
 At times Gerganoff employed Detroit architectural sculptor Corrado Parducci to create sculpture for his buildings.
 R.S. Gerganoff suffered a heart attack while working in the same office that he had worked in since 1927, and died two hours later, on 25 November 1966. He is buried in Highland Cemetery in Ypsilanti.