(written from a Production point of view)
Harmon filmed his scenes for "The City on the Edge of Forever" on Monday 6 February 1967 at Desilu Stage 11 and Wednesday 8 February 1967 at a studio alleyway behind Stage 10. He filmed his scenes for "A Piece of the Action" on Friday 3 November 1967 at Stage 11.
Harmon was an extremely prolific American bit actor. His career spanned seven decades and almost three hundred movie roles and television guest spots, many of them uncredited. Most of his television work was in the 1960s; he was a staple in television of that era.
His television roles included Eddie Halstead on The Rifleman (1958-1962) appearances on The Wild Wild West (1966, with Jon Lormer, Bill Zuckert, and Ed Begley, the father of Ed Begley, Jr.), and as an old hippie on The Odd Couple (1975, with Bill Quinn). In 1969, he appeared again with Vic Tayback in an episode of Land of the Giants, a series which co-starred Don Marshall.
His film credits include the 1939 Buck Rogers serials which were re-edited into a feature film in 1977 (with David Sharpe), The Green Hornet (1944, with Keye Luke), Fear in the Night (1947, with DeForest Kelley), All American (1953, with Morgan Jones and Gregg Palmer), Jail Busters (1955, with Anthony Caruso), God Is My Partner (1957, with John Hoyt), For Love or Money (1963, with Julie Newmar, Leslie Parrish, Willard Sage, and Theo Marcuse), Live Fast, Die Young (1957, with Joseph Mell, Anthony Jochim, Joan Marshall, Dick Crockett and William Windom), Sylvia (1965, with Anthony Caruso, Gene Lyons, Nancy Kovack, Peter Lawford, and Majel Barrett), Texas Across the River (1966, with Michael Ansara, Andrew Prine, George Wallace, Rosemary Forsyth, Dean Martin and Joey Bishop), The Street Is My Beat (1966, written by Harold Livingston), Funny Girl (1968, with Mittie Lawrence and John Warburton), and The Honkers (1972, with Mitch Ryan).
In later years, he retired from the acting business and kept a used books store in Los Angeles. He was a collector of first editions of Mark Twain.
His final role was as Mr. Lipschitz, the Lighthouse Keeper, in The Naked Monster (2005, with Kenneth Tobey and Daniel Roebuck), which was shot ten years prior to the film's completion, a decade after his death.