LOS ANGELES — Hugh O’Brian, who shot to fame as Sheriff Wyatt Earp in what was hailed as television’s first adult Western, has died. He was 91.

A representative from HOBY, a philanthropic organization O’Brian founded, says he died at home Monday morning in Beverly Hills.

Until “The Life and Legend of Wyatt Earp” debuted in September 1955, most TV Westerns — “The Lone Ranger,” “Hopalong Cassidy,” the singing cowboys’ series — were aimed at adolescent boys.

“Wyatt Earp,” on the other hand, was based on a real-life Western hero, and some of its stories were authentic. (The real Earp, who lived from 1848 to 1929, is most famous for his participation in the 1881 “Shootout at the O.K. Corral” in Tombstone, Arizona.)

Critics quickly praised it, and it made O’Brian a star.

“If we were doing Westerns with the chase and the fights that last endlessly, and the sheriff’s daughter in sunbonnet and calico and the Wanted posters ... we wouldn’t reach the audience we reach each week,” O’Brian once said.

“Gunsmoke,” which debuted just a few days after “Wyatt Earp,” became an even bigger hit, and by 1956-57, both were in the top 20 shows. In the 1958-59 season, Westerns accounted for an incredible seven out of the top 10 U.S. television series, including No. 1 “Gunsmoke” and No. 2 “Wagon Train,” with “Wyatt Earp” at No. 10.

“Wyatt Earp” remained a Top 20 hit until 1960, but it was canceled the following year after being supplanted by the avalanche of other adult Westerns.

O’Brian, meanwhile, continued to work frequently in movies, television and theater through the 1990s, although he never again achieved the prominence he enjoyed as Wyatt Earp.

He starred in the 1970s detective series “Search” and appeared in such films as “In Harm’s Way” and “Ten Little Indians,” and reprised his role as Earp in 1994’s “Wyatt Earp: Return to Tombstone,” a film that combined new footage with colorized scenes from the original black-and-white TV show.

Late in his career, O’Brian made frequent guest appearances in television series and variety shows and toured in the national companies of “Cactus Flower,” “1776” and “Guys and Dolls.”

O’Brian had originally planned to study law at Yale University. But after actress Ida Lupino saw him in a play at a small Los Angeles theater she cast him in “Never Fear,” a 1949 film she was directing, and his acting career was launched. He went on to appear in small parts in such films as “The Return of Jesse James,” “Red Ball Express,” “Broken Lance” and “There’s No Business Like Show Business.”

O’Brian was inducted into the Hall of Great Western Performers of the National Cowboy and Western Heritage Museum in 1992.

He also made his mark in philanthropy as founder of the Hugh O’Brian Youth Leadership organization.