Robert Preston Meservey (June 8, 1918 – March 21, 1987) was an American stage and screen actor best-known for his role as Professor Harold Hill in the 1957 musical The Music Man, for which he received the Tony Award for Best Actor in a Musical. He reprised the role in the 1962 film adaptation, and received a Golden Globe Award for Best Actor – Motion Picture Musical or Comedy nomination.

Preston made his Broadway debut in The Male Animal in 1952. He won two Tony Awards for Best Actor in a Musical for The Music Man (1957) and I Do! I Do! (1967) and was Tony-nominated for Mack and Mabel (1975). He co-starred alongside Steve McQueen in the Sam Peckinpah film Junior Bonner (1972). Preston collaborated twice with director Blake Edwards, first in S.O.B. (1981) and again in Victor/Victoria (1982), the latter earning him a nomination for the Academy Award for Best Supporting Actor.

Preston was born Robert Preston Meservey in Newton, Massachusetts, the son of Ruth L. (née Rea) and Frank Wesley Meservey, a garment worker and a billing clerk for American Express. His family moved to Los Angeles in his youth; he graduated from Lincoln High School in January 1935.

Preston appeared in a stock company production of Julius Caesar and a Pasadena Playhouse production of Idiot's Delight. A Paramount Pictures attorney liked his work and recruited him to the studio. The Los Angeles Times reported that Preston's mother was employed by Decca Records, Bing Crosby's label and was acquainted with Crosby's brother Everett, a talent agent; she convinced him to watch one of Preston's performances at the Pasadena Playhouse. The result was a contract with the Crosby agency and a movie deal with Paramount Pictures, Crosby's studio. Preston made his screen debut in 1938, in the crime dramas King of Alcatraz (1938) and Illegal Traffic.

The studio ordered Preston to stop using his family name of Meservey. As Robert Preston, the name by which he was known for his entire professional career, he appeared in many Hollywood films, predominantly but not exclusively Westerns. He was Digby Geste in the sound remake of Beau Geste (1939) with Gary Cooper and Ray Milland, and Dick Allen in the Cecil B DeMille epic Union Pacific. Although not awarded until 2002 due to World War II, the film was the first winner of the Palme d'Or for 1939. He was featured in North West Mounted Police (1940), also with Cooper. He played a Los Angeles police detective in the noir This Gun for Hire (1942).

World War II interrupted Preston's Paramount assignments. Following the Japanese attack on Pearl Harbor, he joined the United States Army Air Forces and served as an intelligence officer in the U.S. 9th Air Force with the 386th Bombardment Group (Medium). At the end of the war in Europe, the 386th and Captain Robert Meservey, an S-2 Officer (intelligence), were stationed in Sint-Truiden, Belgium. Meservey's job had been receiving intelligence reports from 9th Air Force headquarters and briefing the bomber crews on what to expect in accomplishing their missions.

When Preston resumed his movie career in 1947, it was as a freelance character actor, accepting roles for Paramount, RKO, Metro-Goldwyn-Mayer, and various independent producers. Although Preston appeared in many films during this period, he never achieved major stardom. In an interview from 1984, he recalled, "I played the lead in all the 'B' pictures and the villain in all the epics. After a while, it was clear to me I had sort of reached what I was going to be in movies." During the 1950s, Preston found additional roles in television.

Preston is probably best known for his performance as Professor Harold Hill in Meredith Willson's musical The Music Man (1957). He had appeared on stage, but it was his first musical. "They'd run through all the musical comedy people before they cast me", he remembered years later. He won a Tony Award for his performance.