LOS ANGELES (AP) – Actor Pernell Roberts, who shocked Hollywood by leaving the TV Western 'Bonanza' at the height of its popularity, then found fame again years later on 'Trapper John, MD', has died. He was 81.

Roberts, the last surviving member of the classic Western's cast, died of cancer on Sunday at his Malibu home, his wife Eleanor Criswell told the Los Angeles Times.

Although he rocketed to fame in 1959 as Adam Cartwright, eldest son of a Nevada ranching family led by Lorne Greene's patriarchal Ben Cartwright, Roberts chafed at the limitations he felt his 'Bonanza' character was given.

"They told me the four characters (Greene, himself and Dan Blocker and Michael Landon as his brothers) would be carefully defined and the scripts carefully prepared," he complained to The Associated Press in 1964. "None of it ever happened."

It particularly distressed him that his character, a man in his 30s, had to continually defer to the wishes of his widowed father.

"Doesn't it seem a bit silly for three adult males to get Father's permission for everything they do?" he once asked a reporter.

Roberts agreed to fulfil his six-year contract but refused to extend it, and when he left the series in 1965, his character was eliminated with the explanation that he had moved away.

'Bonanza', with its three remaining stars, continued until 1973, making it second to 'Gunsmoke' as the longest-running Western on TV. Blocker died in 1972, Greene in 1987, and Landon in 1991.

When Roberts left the show the general feeling in Hollywood was that he had foolishly doomed his career and turned his back on a fortune in 'Bonanza' earnings.

Indeed, for the next 14 years he mainly made appearances on TV shows and in miniseries, or toured with such theatrical productions as 'The King and I', 'Camelot' and 'The Music Man'.

His TV credits during that time included 'The Virginian', 'Hawaii Five-O', 'Mission Impossible', 'Marcus Welby, MD', 'Banacek', 'Ironside' and 'Mannix'.

Then, in 1979, he landed another series, 'Trapper John, MD', in which he played the title role.

The character, but little else, was spun off from the brilliant Korean War comedy-drama 'M-A-S-H', in which Wayne Rogers had played the offbeat Dr. (Trapper) John McIntire opposite Alan Alda's Dr. Benjamin Franklin (Hawkeye) Pierce.

Rogers had left that series after just three seasons.

In 'Trapper John, MD', the Korean War was nearly 30 years past and Roberts' character was now a balding, middle-aged chief of surgery at San Francisco Memorial Hospital.

He no longer fought the establishment, having learned how to deal with it with patience and wry humour.

The series, praised for its serious treatment of the surgical world, aired until 1986.

Roberts' other venture into series TV was 'FBI: The Untold Stories' (1991-1993), in which he acted as host and narrator.

Pernell Roberts, Jr. was born in 1928 in Waycross, Georgia. After pursuing occupations that ranged from tombstone maker to railroad riveter, he decided to become an actor.

Roberts worked extensively in regional theatres, then gained notice in New York, where he won a Drama Desk award in 1956 for his performance in an off-Broadway production of 'Macbeth'.

He eventually moved to Hollywood, where he appeared in several TV shows and landed character roles in such features as 'Desire Under the Elms', 'The Sheepman' and 'Ride Lonesome' until 'Bonanza' made him a star.

Three of Roberts' marriages ended in divorce. His first, to Vera Mowry, produced a son, Jonathan, who died in 1989 at age 37.