Jean-Claude van Itallie, a playwright, director and performer who was a mainstay of the experimental theater world and who was especially known for “America Hurrah,” a form-bending trio of one-acts that opened in 1966 in the East Village and ran for more than 630 performances, died on Sept. 9 in Manhattan. He was 85.

His brother, Michael, said the cause was pneumonia.

Beginning in the late 1950s, Mr. van Itallie immersed himself in the vibrant Off Off Broadway scene, where playwrights and performers were challenging theatrical conventions. He joined Joseph Chaikin’s newly formed Open Theater in 1963, and his first produced play, “War,” was staged in the West Village. He was a favorite of Ellen Stewart, who had founded La MaMa Experimental Theater Club in 1961.

Mr. van Itallie’s early works, including components of what became “America Hurrah,” were generally performed in lofts and other small spaces, but for the full-fledged production of “America Hurrah,” in November 1966, he moved up to the Pocket Theater on Third Avenue. The work caused a sensation.

“I think you’ll be neglecting a whisper in the wind if you don’t look in on ‘America Hurrah,’” Walter Kerr began his rave review in The New York Times. “There’s something afoot here.”

The first play in the trilogy, “Interview,” looked at the dehumanizing process of job hunting. In the second, “TV,” a commentary on mass media’s ability to trivialize, three people in a television ratings company watch a variety of shows; gradually the ones they’re watching take over the stage, and the three “real” people are absorbed into them.

The third piece was “Motel,” which was first performed in 1965 at La MaMa E.T.C. and which the script describes as “a masque for three dolls.” (Robert Wilson, still early in his groundbreaking career, designed the original set.) Writing about a London production of “America Hurrah” for The Times in 1967, Charles Marowitz called it “a short but stunning masterpiece.”

In it, a monstrous doll, the “Motel-keeper,” presides over a motel room and emits a stream of increasingly arcane patter. Two other dolls arrive at the room and proceed to trash it, scrawling vulgar graffiti on the wall and eventually dismantling the Motel-keeper.

In 1993, when the Dobama Theater in Cleveland Heights, Ohio, mounted a revival of “America Hurrah,” Marianne Evett, theater critic for The Plain Dealer of Cleveland, reflected on its original impact.

“When it opened,” she wrote, “it rocketed to fame, announcing that a new kind of American theater had arrived — deliberately experimental, savagely funny, politically aware and critical of standard American life, its institutions and values.”

Mr. van Itallie continued making new work for more than half a century, and also founded Shantigar, a retreat in western Massachusetts, where he nurtured aspiring theater artists. Just two years ago, La MaMa staged the premiere of his new play, “The Fat Lady Sings,” about an evangelical family.

“Jean-Claude van Itallie was an artist who was constantly questioning and digging into the deeper realms of our human existence and spirit,” Mia Yoo, artistic director of La MaMa, said by email. “In this moment of change it is artists like Jean-Claude whom we must look to.”

Jean-Claude van Itallie was born on May 25, 1936, in Brussels to Hugo and Marthe (Levy) van Itallie. The family left Belgium as the Nazis advanced on the country in 1940, and by the end of the year they had reached the United States. They settled in Great Neck, on Long Island. Hugo van Itallie had been a stockbroker in Brussels and resumed that career on Wall Street.

Jean-Claude’s parents spoke French at home, something that influenced his later approach to theater, he said.

“I had the good fortune to grow up in a couple of languages,” he said, “and I think that makes you realize that no single language contains reality, that words are always an approximation of reality, that language and even thought are perspectives on reality, not reality itself.”

He was active in the drama club at Great Neck High School and in student productions at Deerfield Academy in Massachusetts, where he spent his senior year. In 1954, he enrolled at Harvard University, where he continued to study theater and wrote his first one-act plays before graduating in 1958. His honors thesis was titled “The Pessimism of Jean Anouilh,” the French dramatist.

Mr. van Itallie settled in Greenwich Village. He worked for several years adapting and writing scripts for television, particularly for “Look Up and Live,” a Sunday morning anthology program on religious themes broadcast on CBS. It was a period when many TV shows had corporate sponsors that had to be appeased, but his wasn’t one of them; “Look Up and Live” gave the writers a measure of freedom.

“All you had to do was please God and CBS,” he said.

He was continuing to write plays on his own. “Motel,” the third piece of the “America Hurrah” trilogy, was actually the first to be written, in 1961 or ’62.

“I was about three years out of Harvard, living in Greenwich Village and knocking on the door of Broadway theater,” he told The Plain Dealer decades later. “And I wasn’t getting in. I think that ‘Motel’ grew out of my anger — partly at that situation, but probably a much deeper anger at the way my mind had been conventionalized and conditioned. It just rose up out of me.”

The success of “America Hurrah” in New York spawned other productions, though they sometimes ran into resistance, including in London, where the graffiti scrawled in “Motel” offended censors. In Mobile, Ala., a production by the University of South Alabama at a city-owned theater in 1968 was shut down by the mayor, Lambert C. Mims, after two performances.

“It is filth, pure and simple,” the mayor said, “and I think it is a crying shame that Alabama taxpayers’ money has been used to produce such degrading trash.”

Among Mr. van Itallie’s other works with Open Theater was “The Serpent,” a collaborative piece inspired by the book of Genesis that he shaped into a script. It was first performed in Rome during a European tour in 1968 and later staged in New York.

In the 1970s Mr. van Itallie became known for translations.

“I did my work as a playwright backwards,” he once said, “creating new theatrical forms in the ’60s, and in the ’70s going back to study masters like Chekhov.”

Later still he did some acting, including performing a one-man autobiographical play called “War, Sex and Dreams,” which related his childhood escape from the Nazis, his life as a gay man and how he coped with sudden fame in the 1960s. D.J.R. Bruckner reviewed a performance of the work at the Cafe at La MaMa in 1999 for The Times, calling it the “often amusing and often sad confession of a man in his 60s whose heart is lonely and who teases one into wondering what, despite his remarkable candor, he is leaving out.”

Mr. van Itallie split his time between a home in Manhattan and the farm in Rowe, Mass., which is home to his Shantigar Foundation. In addition to his brother, he is survived by his stepmother, Christine van Itallie.

In remembering Mr. van Itallie, Ms. Yoo called to mind her predecessor, Ms. Stewart, who died in 2011.

“I think of Ellen Stewart and him looking down at us and insisting that we move and make change,” she said.