Pernell Roberts, the high-minded stage actor who found fame, but also discontent, as one of the original stars of "Bonanza," died Jan. 25, 2010, at his home in Malibu, CA. He was 81. The cause was pancreatic cancer. Pernell Elven Roberts Jr. has several years of intense New York stage experience under his belt when he became known to the country as Adam Cartwright, the eldest of the Cartwright boys born to father Lorne Greene on the long-running television western "Bonanza." He dove into the thriving Off-Broadway scene in the mid-1950s, after graduating from the University of Maryland. Muscular, handsome and forthright, he played Antonio in Twelfth Night, Mercutio in Romeo and Juliet, and the title role in Macbeth, winning a 1956 Drama Desk Award for the latter. On Broadway, he was Petruchio in The Taming of the Shrew (1957) and the villainous Bosola in The Duchess of Malfi, both in 1957 and productions of American Shakespeare Festival Theatre. That same year, he appeared in A Clearing in the Woods by Arthur Laurents.

Accustomed as he was to a rigorous diet of the classics, it was perhaps not surprising that, despite enormous success, he bolted from "Bonanza" after the 1964-65 season, criticizing the show's simple-minded content and lack of minority actors. He also hated his character calling Lorne Greene "Pa," as both were adult men, and asked to stop wearing his toupee. The show soldiered on, remaining popular until its end in 1973. Mr. Roberts never returned.

"I had six seasons of playing the eldest son on that show," he once said. "Six seasons of feeling like a damned idiot, going around — me, like a middle-aged teenager, saying, 'Yes, Pa,' 'No, Pa' on cue. It was downright disgusting — such dialogue for a grown man. I felt I wasn't being taken seriously as an actor, and that's like death to one's talent."

He occupied the ensuing years with guest shots on shows such as "The Odd Couple," "Mannix," "The Wild Wild West" and "Gunsmoke." He again found television fame, of a somewhat more serious vein, as the star of the medical drama "Trapper John M.D.," which ran from 1979 to 1986. He was nominated for an Emmy Award in 1981.

He also returned to the stage from time to time, and was nominated for a 1973 Joseph Jefferson Award for his performance in Welcome Home, at the Ivanhoe Theatre in Chicago.

Mr. Roberts was married four times. His first wife was Vera Mowry, a professor who, for 50 years, was a fixture at the theatre department at Hunter College, teaching theatre history. More than ten years Mr. Roberts' senior, Mowry, who had been a professor at Washington State University, and the actor married in 1951. Both took part in the initial seasons of Washington DC's Arena Stage, one of the first important regional theatres in America. There, he acted in The Playboy of the Western Word, The Glass Menagerie, and The Importance of Being Earnest, among others.

With Mowry, Mr. Roberts had his only child, Jonathan Christopher Roberts. By the time Mr. Roberts moved to New York in 1953, the two had separated. His son died in a motorcycle accident in 1989 at age 38. He was married to Eleanor Criswell at the time of his death. She survives him.