John Truman Mantley (April 25, 1920 – January 14, 2003) was a Canadian theatrical actor, writer, director, screenwriter and producer of the long-running television series, Gunsmoke.
Van Manzer met his wife Violet Petello in 1906 in New York City at the casting of The Convict's Daughter, directed by Maurice Costello.
In later years Van Manzer operated a traveling circus while his wife ran a number of concession stands in a park across the lake from Toronto.
Mantley trained as a fighter pilot in the Royal Canadian Air Force during World War II, and was sent to England and India.
He had planned to work for Mary Pickford following graduation from Pasadena Playhouse, but she sold both her production companies when it appeared there was no future for the motion picture industry.
During his time at WOR, Mantley began to write for television and edited scripts from university students because the station could not afford a writer.
He then spent four years in Rome, where he produced and directed a series of 39 successful half-hour dramatic anthologies for American television, a pioneering effort which played in some 200 markets.
The first of Mantley's three children was born in Italy, where the couple managed to financially survive because John's wife Angela did the voiceovers—post synchronization of the voices of Gina Lollobrigida and Sophia Loren, among others.
At Mary Pickford's urging, he then wrote The Snow Birch, which was produced by 20th Century Fox as Woman Obsessed starring Susan Hayward.
He also wrote for Harrigan and Son, The Untouchables, The Outer Limits, Kraft Theatre, Rawhide, and freelanced scripts for Gunsmoke, the longest running dramatic show in television history, which he produced for the next ten years.