The cause was a heart ailment, said Steve Rhodes, chief deputy coroner of Canyon County, Idaho.
In a career spanning more than 175 films and television credits, Mr. Kennedy was among the most dependable and versatile performers in Hollywood. Whether malevolent, earnest, or serving as comic relief, he held his corner of the screen opposite charismatic movie stars including Cary Grant, Paul Newman, John Wayne, and James Stewart.
The son of entertainers, Mr. Kennedy was a child actor on the radio and then spent about 15 years in the Army before reemerging in show business in the late 1950s playing a military police officer on the CBS sitcom ''The Phil Silvers Show.''
Mr. Kennedy, who stood 6 foot 4 inches and weighed 300 pounds, made his screen debut as a rebel soldier opposite Kirk Douglas in ''Spartacus'' (1960). His most important early film was Stanley Donen's ''Charade'' (1963), which starred Grant and Hepburn and was an engaging blend of suspense, romance, and sophisticated comedy set in Paris.
Mr. Kennedy played one of the World War II veterans who tries to frighten a recent widow (Hepburn) into revealing where her late husband stashed money stolen during the war.
Film historian Jeanne Basinger said Mr. Kennedy ''can ride that fine line between very scary menacing villain and fitting in with a lighter-hearted comic mode. He had the ability to give subtle variations on his basic persona — he could shade it toward comedy, shade it away from comedy. He could live as himself in the universe of the film. This is a movie career — steady.''
Indeed it was steady, and Mr. Kennedy remained a welcome presence even if the movies were not always of the highest caliber. After ''Charade,'' Mr. Kennedy played heavies in ''Hush . . . Hush, Sweet Charlotte'' and ''Straightjacket'' (both 1964). During the next several years, he had supporting parts in dramas including ''Shenandoah,'' ''The Flight of the Phoenix,'' and ''The Sons of Katie Elder.'' He was a gruff major in the popular war film ''The Dirty Dozen.''
Mr. Kennedy's breakthrough performance was in ''Cool Hand Luke'' (1967), which starred Newman as a self-described ''hard case'' who gets sent to a Southern chain gang for cutting the heads off parking meters. Mr. Kennedy played the veteran convict Dragline, who at first sees Luke as a threat to his authority and nearly kills him in a boxing ring.
''Yeah, I beat up Paul Newman and alienated every woman in America,'' Mr. Kennedy later quipped.
New York Times film critic Bosley Crowther wrote that Mr. Kennedy was ''powerfully obsessive as the top dog who handles things his way as effectively and finally as destructively as does the warden or the guards.''
After the success of ''Cool Hand Luke,'' Mr. Kennedy's fee shot from $20,000 to $200,000 per movie. He began a run of lawmen characters in films such as ''Hurry Sundown'' (1967), the first-rate manhunt drama ''The Boston Strangler'' (1968), and ''. . .Tick. . .Tick. . .Tick'' (1970).
Mr. Kennedy popped up in a variety of westerns, including ''Fools' Parade'' (1971) with Stewart and ''Cahill U.S. Marshal'' (1973) with Wayne.
He had supporting parts in two Clint Eastwood dramas, as a foul-tempered crook in ''Thunderbolt and Lightfoot'' (1974) and as a mountain climber in the spy thriller ''The Eiger Sanction'' (1975). He coasted through a series of action and disaster films such as ''Earthquake'' (1974) and the four ''Airport'' movies based on Arthur Hailey's best-selling novel.
Over the course of the ''Airport'' films, Mr. Kennedy's character, Joe Patroni, transitions from salty maintenance chief to cocksure Concorde pilot. The deadpan earnestness of the series bordered on self-parody by the last installment, in which pilot Patroni opens the window of the supersonic Concorde and shoots a flare to divert an onrushing ballistic missile.
''Airport'' helped inspire the Zucker Brothers' antic ''Airplane!'' satire, in which the filmmakers hoped to cast Kennedy as the bumbling plane dispatcher. The role went to Lloyd Bridges because Kennedy ''couldn't kill off his 'Airport' cash-cow,'' Jerry Zucker told the London Guardian in 2010.
The Zucker brothers, Jerry and David, eventually hired Mr. Kennedy to play his authoritative presence for laughs in ''The Naked Gun'' (1988). He portrayed Captain Ed Hocken, the dim-witted boss of the pratfall-prone detective played by Leslie Nielsen. Mr. Kennedy also appeared in two ''Naked Gun'' sequels.
George Harris Kennedy Jr. was born in New York City. He was a toddler when his father, a bandleader, died. He was raised by his mother, a dancer, and spent much of his childhood acting on children's radio productions.
He served in the Army Air Forces in Europe during World War II, then was assigned to the Armed Forces Radio and Television Service. Despite Army policy against officers going on air, then-Captain Kennedy used a pseudonym to broadcast on a station in Seoul.
A back injury led to his discharge. He became a technical adviser and actor on ''The Phil Silvers Show,'' the comedy set on an Army base.
He later starred on two short-lived series: ''Sarge'' (NBC, 1971-72) as a policeman-turned-priest, and ''The Blue Knight'' (ABC, 1975-76), based on Joseph Wambaugh's novel about a cop on the beat. From 1988 to 1991, Mr. Kennedy appeared on CBS's soap opera ''Dallas'' as a rival to Larry Hagman's Machiavellian oil magnate J.R. Ewing.
Mr. Kennedy's marriage to Revel Wurman ended in divorce. In 1978, he married Joan McCarthy. In addition to several children, he helped raise a granddaughter whose mother had drug problems.
His memoir, ''Trust Me,'' was published in 2011. That year, he told Smashing Interviews Magazine that a lonely childhood led him to a career in entertainment.
''Acting is beautiful,'' he said. ''If I'm prejudiced toward doing it, it is because of the joy that I derive from it. Add that to the fact that I didn't have any other choices. I either talked to myself, or I didn't talk to anybody.''