According to a biography on his personal website, Hardin was born Orison Whipple Hungerford Jr.on New Year’s Day, 1930, in New York City. The name Whipple was given to him in honor of an ancestor on his father’s side, William Whipple of New Hampshire, one of the signers of the Declaration of Independence.
After being discovered by a talent scout while renting a Halloween cowboy outfit at Western Costume on Melrose Avenue near Paramount Pictures, he was given a contract at Paramount, where he made six films. He then talked with John Wayne about starring opposite him in Rio Bravo, but the part went to Ricky Nelson. Still, his discussions with Wayne bore fruit in the form of a TV deal with Warner Bros., and his run on Cheyenne began in 1958, when he replaced star Clint Walker, who was in a contract dispute with Warner Bros. Walker returned to the series in 1959, and Hardin moved on to Bronco, which aired until 1962.
Later, he appeared in films including The Battle of the Bulge and PT 109, the latter of which detailed John F. Kennedy’s war service.
Eventually, Hardin spent several years in Europe before returning to a Hollywood that had dramatically changed in the late 1960s and 1970s. He decided to quit acting and enter the ministry, affiliating with Calvary Chapel.