James Arness, who burnished the legend of America’s epic West as Marshal Matt Dillon, the laconic peacemaker of Dodge City on “Gunsmoke,” one of the longest-running dramatic series in television history, died on Friday at his home in Los Angeles. He was 88.

A family spokeswoman, Ginny Fazer, confirmed the death. Mr. Arness was terribly shy and had almost no training as an actor. A wartime leg wound made it painful for him to mount a horse. But he became the best-known tin star of his era, portraying the towering, weathered marshal for 20 years, from 1955 to 1975. He also made some 50 films and television movies, mostly westerns, in a career that stretched across five decades.

To a generation of television viewers, Mr. Arness and “Gunsmoke” embodied a new, more adult vision of the mythic Old West: a quiet, vulnerable lawman facing not stereotyped villains and clichéd situations but a chaotic frontier freighted with moral judgments and occasional failure. He might be too late to stop a killing. He could save a girl from kidnappers, but not from her father’s brutality.

Audiences had long been accustomed to western heroes who never were, having been sanitized by the trail songs of Gene Autry and Roy Rogers and the righteous gunplay of the Lone Ranger and Hopalong Cassidy . But Marshal Dillon never got the girl, did not love his horse, wore only one gun and fired it reluctantly, usually drawing last but shooting straightest in dusty street duels. Over the years, the marshal was shot 30 times.