Jacques Joseph O'Mahoney (February 7, 1919 – December 14, 1989), known professionally as Jock Mahoney, was an American actor and stuntman. He starred in two action/adventure television series, The Range Rider and Yancy Derringer. He played Tarzan in two feature films and was associated in various capacities with several other Tarzan productions. He was credited variously as Jacques O'Mahoney, Jock O'Mahoney, Jack Mahoney, and finally Jock Mahoney.

Mahoney was born February 7, 1919, in Chicago, Illinois and reared in Davenport, Iowa. He was of French and Irish descent, the only child of Ruth and Charles O'Mahoney. He entered the University of Iowa in Iowa City and excelled at swimming and diving, but dropped out to enlist in the United States Marine Corps when World War II began. He served as a pilot and flight instructor.

After his discharge from the Marine Corps, Mahoney moved to Los Angeles, and for a time was a horse breeder. However, he soon became a movie stuntman, doubling for Gregory Peck, John Wayne, and Errol Flynn. For the climactic fight scene in Flynn's 1948 film Adventures of Don Juan, "Errol wanted to make a leap from midway up the staircase to the floor below," recalled director Vincent Sherman in his memoir, "but we had trouble finding a double willing to try it. Frank Pattison, our unit manager, said there was only one man in Hollywood who could do it: Jock Mahoney." Mahoney demanded and received $1,000 for the dangerous stunt. "It was a spectacular leap," wrote Sherman. "I should have shot it in slow motion to show Mahoney sailing through the air, but I didn't, and every time I see the film I want to kick myself."

Most of Mahoney's films of the late 1940s and early 1950s were produced by Columbia Pictures. Like many Columbia contract players, Mahoney worked in the studio's two-reel comedies. Beginning in 1947, writer-director Edward Bernds cast Mahoney in slapstick comedies starring the Three Stooges. Mahoney had large speaking roles in these films, and often played his scenes for laughs. Often cast alongside heroine Christine McIntyre, he appeared in the Stooge films Out West (1947), Squareheads of the Round Table (1948) (and its 1954 remake, Knutzy Knights), Fuelin' Around (1949), and Punchy Cowpunchers (1950). In the Stooge films, Mahoney—striking a heroic pose—would suddenly get clumsy, tripping over something or taking sprawling pratfalls.

Beginning in 1950, Columbia management noticed Mahoney's acting skills and gave him starring roles in two adventure serials, Cody of the Pony Express (1950) and Roar of the Iron Horse (1951). Mahoney succeeded stuntman Ted Mapes as the double for Charles Starrett in Columbia's The Durango Kid Western series. Starrett recalled that everyone called the young stuntman "Jocko": "I certainly had the best stuntmen. Jocko was just beautiful. Like a cat."

The Durango Kid wore a mask covering much of his face, enabling Mahoney to replace Starrett in the action scenes. Mahoney's daring stunts made it seem that the older Starrett grew, the more athletic he became. Mahoney contributed so much to this series that he was awarded featured billing and major supporting roles as well, first as villains and then as sympathetic characters. By 1952 Columbia was billing him as "Jack Mahoney".

When Charles Starrett's contract ran out in the spring of 1952, Columbia decided to replace him with Mahoney, opposite Starrett's sidekick Smiley Burnette. The first film was completed but never released; Columbia abandoned the series in June 1952, bringing an end to its long history of B-Western production.

Cowboy star Gene Autry, then working at Columbia, hired Mahoney to star in a television series. Autry's Flying A Productions filmed 79 half-hour episodes of the syndicated The Range Rider from 1951 to 1953. In 1959, a lost episode was shown six years after the series ended. He was billed as Jack Mahoney. The character had no name other than Range Rider. His series co-star was Dick Jones, playing the role of Dick West.