Nicol Williamson, a Scottish-born theater star heralded as one of the finest actors of his generation but whose menacing unpredictability onstage and off diminished his career, died Dec. 16 in Amsterdam of esophageal cancer. He was 75.

His son, Luke Williamson, confirmed the death to the Associated Press. Mr. Williamson had lived in the Netherlands for more than two decades. The news of his death was reportedly delayed at the actor’s wish to die anonymously — an understated ending to a stormy life.

Mr. Williamson was a galvanic presence in dozens of stage and film roles and drew favorable comparisons with Laurence Olivier and Charles Laughton.

Author Samuel Beckett pronounced him “touched by genius.” The British playwright John Osborne, who made Mr. Williamson a marquee name in the 1964 drama “Inadmissible Evidence,” considered him “the greatest actor since Marlon Brando.”

With his nasally twang, receding ginger hair, despairing eyes and hangdog face, Mr. Williamson had little of the young Brando’s beauty and raw physical power. He compensated with a demeanor that conveyed cunning, an explosive temperament and a general aura of sweaty self-loathing.

Nicol Williamson, in an undated photo, was hailed as one of the finest actors of his generation, but his unpredictability onstage and long absences from his profession diminished his career trajectory. (The Washington Post)

These traits were on display in Mike Nichols’s 1974 staging of Anton Chekhov’s “Uncle Vanya,” for which Mr. Williamson in the title role won the Tony Award for best actor.

Onscreen, Mr. Williamson excelled as a cocaine-addicted Sherlock Holmes in “The Seven-Per-Cent Solution” (1976), a ruthless Afrikaaner policeman in apartheid South Africa in “The Wilby Conspiracy” (1975) and the wizard Merlin in director John Boorman’s violent retelling of the King Arthur legend in “Excalibur” (1981).

Willfully or not, Mr. Williamson seemed determined to torpedo his reputation through heavy drinking and erratic, often abusive behavior.

Coming to the defense of a stage director, Mr. Williamson threw beer on the notoriously cruel theater impresario David Merrick and then punched him. Other stories, perhaps embellishing the incident, have Mr. Williamson tossing Merrick in the trash. Mr. Williamson later quipped, “The funny thing was that nobody in his entourage tried to attack me or help him.”

Mr. Williamson’s notoriety for turbulent antics resurfaced while he starred as King Henry VIII of England in the 1976 Broadway musical “Rex.” It ran 48 performances and was best remembered for Mr. Williamson slapping another actor for talking when Mr. Williamson was taking his bow during curtain call.

The two incidents might have been written off had Mr. Williamson not whacked the actor Evan Handler with a sword when they were starring on Broadway in Paul Rudnick’s 1991 comedy “I Hate Hamlet.” Mr. Williamson played the ghost of John Barrymore, the highly gifted, randy and alcoholic actor of the early 20th century.

During a sword fight with Handler, Mr. Williamson appeared to improvise lines: “Put some life into it! Use your head! Give it more life!” Handler walked offstage, and Mr. Williamson broke the awkward silence by turning to the audience and asking, “Well, should I sing?”

In the remaining few months of the show, which received mixed reviews, Mr. Williamson continued ab-libbing to the audience. One night, he told them, according to Rudnick, “Head home and enjoy a nice juicy slice of sexual intercourse.” Other nights he denigrated the critics, the same group of writers who had once propelled him to the top of his profession.

The son of a foundry worker, Nicol Williamson was born Sept. 14, 1936, in the Scottish mining town of Hamilton and raised in Birmingham, England. He appeared in repertory theater before joining London’s Royal Shakespeare Co. in 1962.

He dazzled audiences with his versatility and his ability to play much older characters convincingly. He was frequently mentioned as a leader among a crop of promising young talent that included Albert Finney, Anthony Hopkins and Ian McKellen.

The performance that sealed Mr. Williamson’s prominence was the alcoholic, morally disintegrating lawyer Bill Maitland in Osborne’s “Inadmissible Evidence” (1964).

Critic Ronald Bryden wrote in the New Statesman that Mr. Williamson, not yet 30, “fills every cranny of Maitland’s portrait with knowledge: the nervous sweating, the lurching jocularity, the sick waves, tangible as nausea, of self-disgust.”

The show reached Broadway in 1965 and earned Mr. Williamson a Tony nomination. (A bowdlerized 1968 film version of “Inadmissible Evidence” that also starred Mr. Williamson tanked commercially and critically.)

After the first jolt of fame with “Inadmissible Evidence,” Mr. Williamson mystified his peers and his friends by turning down offers to work with directors of the caliber of Olivier and Ingmar Bergman.

Mr. Williamson said he preferred short-run jobs, like reading poems by T.S. Eliot set to jazz. Explaining his motivations, he later told the New York Times, “Too much acting can make you a worse actor. Actors who do play after play tend to rely on bad habits or technique and do shoddy work.”

Yet he repeatedly bobbed back into the public eye with startling performances, including a portrayal of Hamlet as a scruffy peasant in a 1969 stage and film version directed by Tony Richardson.

From the 1970s to the 1990s, Mr. Williamson alternated among film, television and stage roles. He portrayed Little John to Sean Connery’s Robin Hood and Audrey Hepburn’s Lady Marian in “Robin and Marian” (1976), and had the title role in the public television miniseries “Lord Mountbatten: The Last Viceroy” (1986). Increasingly, he accepted mediocre assignments in movies, including “The Exorcist III” (1990) and “Spawn” (1997).

His marriage to actress Jill Townsend ended in divorce. Survivors include their son.

In a career of peaks and valleys, one of Mr. Williamson’s most captivating moments in show business was his command performance at the Nixon White House in 1970. He had been recommended to the president by British Prime Minister Harold Wilson, who admired Mr. Williamson’s interpretation of Hamlet.

Before hundreds of dignitaries at the White House, Mr. Williamson recited soliloquies and songs from Shakespeare, passages from Arthur Miller’s “Death of a Salesman,” doggerel from Robert Benchley and poetry from e.e. cummings and William Butler Yeats.

When the formal part of the evening was over, the first couple retreated to bed. Mr. Williamson stayed, belting out Tin Pan Alley tunes backed by a jazz band.

“This should be an evening that swung!” Mr. Williamson told the remaining crowd. “We should all have fun and everybody get boozed. And I hope we don’t wake the people upstairs.”