Los Angeles ? It takes a special kind of lawman to carry on for 20 years in the Wild West of TV.

Matt Dillon, the mythical marshal of Dodge City, stood tall — all 6 feet, 6 inches of him — on “Gunsmoke” from 1955 to 1975. He outlasted dozens of other Western heroes while making history on TV’s longest-running dramatic series, a record that held until NBC’s “Law & Order” tied the CBS Western’s record in 2010.

Through all those gunslinging years, James Arness, who died Friday, kept Marshal Dillon righteous, peace-seeking and, most of all, believable.

Fickle viewers can kill a TV hero as surely as a bullet from an outlaw’s six-gun. But Arness knew how to maintain order not only in circa-1870s Dodge City, but also among the TV audience, whose itchy fingers on their channel changers he knew how to calm.

In an era when TV actors typically chewed the scenery, Arness had a credible, commanding presence by hardly uttering a word. A typical scene found a dozen cowboys riding up to the town jail intent on busting out a prisoner pal.

Dillon faces them all down.

“The first move anybody makes,” he says, with a slight shake of his head, “I cut you in two.”

Arness’ defiant but rueful delivery is so understated, he makes Clint Eastwood seem like a loudmouth.

No wonder “Gunsmoke” wore so well. And became the last word on a programming craze that some seasons found as many as 30 Westerns on the air. When “Gunsmoke” went off in 1975, it was the only Western left.

By the end of his career, Arness, who was 88 when he died at his home in the Brentwood section of Los Angeles, seemed almost indistinguishable from Matt Dillon in the audience’s mind.

Befitting Marshal Dillon’s dignity and composure, Arness wrote, and left behind, a simple, straight-from-the-heart farewell which, at his request, was posted posthumously Friday on his official website.

“I had a wonderful life and was blessed with … (so) many loving people and great friends,” he said, then went on to thank his multitude of fans.