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.
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.
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.
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.
Pernell Roberts Jr was born in 1928. After pursuing occupations that ranged from tombstone maker to railway riveter, he decided to become an actor.
Three of Roberts' marriages ended in divorce. His first, to Vera Mowry, produced a son, Jonathan, who died in 1989 aged 37.