Following his graduation from the University of Iowa and World War II service, Jock Mahoney came to Hollywood as a stuntman. Quickly establishing a reputation as one of the best and most courageous purveyors of his trade, Mahoney graduated to speaking roles in 1946. Billed as Jacques O'Mahoney, he played villains and secondary roles in Republic and Columbia westerns, showed up as a parodied "strong and silent" leading man in a handful of Three Stooges 2-reelers, and, while doubling for Errol Flynn, performed the legendary staircase leap in 1949's The Adventures of Don Juan.
In 1951, Gene Autry hired Mahoney (who was now billing himself as Jack Mahoney) to star in the popular TV western series The Range Rider. This led to leading roles in such features as Overland Pacific (1954), Showdown at Abilene (1956) and I've Lived Before (1956). In 1958, Mahoney starred in another weekly TV western, Yancey Derringer. Two years later he played the villain in a Tarzan picture starring Gordon Scott, succeeding Scott as the "lord of the jungle" in Tarzan Goes to India (1962) -- during the filming of which he fell deathly ill, a fact that is painfully obvious in the completed picture.
Suffering a severe stroke in 1973, Mahoney made a near-complete recovery in the last five years of his life, performing his final stunt (tumbling from a wheelchair) in Burt Reynolds' The End. Reynolds exhibited his admiration for Mahoney in his 1980 vehicle Hooper, in which the stuntman character played by Brian Keith was named "Jocko." Mahoney's last film work was as stunt coordinator for John Derek's otherwise wretched 1981 remake of Tarzan of the Apes. Married for many years to actress Mary Field, whom he'd met while filming Range Rider, Jock Mahoney was the stepfather of Oscar-winning actress Sally Field.