Richard Foreman, the relentlessly teasing, deliberately mysterious avant-garde playwright and impresario who founded the Ontological-Hysteric Theater, won a bookshelf full of Obie Awards and received a MacArthur fellowship in his late 50s, died on Saturday in Manhattan. He was 87.

David Herskovits, the artistic director of Target Margin Theater in Brooklyn and a co-executor of Mr. Foreman’s literary estate, said the death, at Mount Sinai West Hospital, was from complications of pneumonia.

Mr. Foreman established his company in 1968 and went on to present more than 50 of his own plays; for many years the group was housed at St. Mark’s in the Bowery, the historic East Village church. The company name refers to the metaphysical study of the nature of existence and to Mr. Foreman’s conviction that the situations he worked with were, as he told John Rockwell of The New York Times in 1976, “basically hysteric — repressed passions emerging as philosophical interactions.”

The titles of his plays hinted at his worldview. “Dream Tantras for Western Massachusetts” (1971) was one of numerous collaborations with the composer Stanley Silverman. “My Head Was a Sledgehammer” (1979) depicted a professor and two students facing the frustrations of acquiring knowledge. “Bad Boy Nietzsche!” (2000) was about that German philosopher’s nervous breakdown. “King Cowboy Rufus Rules the Universe!” (2004) was inspired by the George W. Bush administration.

Other titles, like “Total Recall” (1970), “Vertical Mobility” (1974) and “Permanent Brain Damage” (1996), were more concise but no less resonant.

Mr. Foreman’s plays tended to be “peerless mini-extravaganzas” offering “dizzying theatrical joys,” Ben Brantley wrote in one 2004 Times review. Looking at Mr. Foreman’s body of work, he also mentioned the familiar “cross-cultural medley of musical fragments, the strings and poles that segment the stage, vulnerable baby dolls and menacing thugs in animal outfits.”

The same review called Mr. Foreman’s strength as a writer “his refusal to spell anything out.”

Mr. Foreman was recognized and rewarded early in his career. He received his first Obie Award in 1970, sharing it with Mr. Silverman, for “Elephant Steps,” which has sometimes been described as an opera about a radio show. It had its premiere at the Tanglewood music festival in Massachusetts in 1968.

When “Elephant Steps” came to Hunter College in Manhattan two years later, the chief classical music critic of The Times, Harold C. Schonberg, found it “all very chic,” but he also confessed, “I don’t know what the hell was going on.”

Mr. Foreman went on to win a half-dozen more Obies, first in 1973 for the Ontological-Hysteric Theater itself, then in 1976 for “Rhoda in Potatoland,” a nearly two-hour one-act show about a woman having bizarre dreams.

On two occasions he won Obies for best play in the same year — meaning that he essentially tied with himself for the top award: for “The Cure” (with an emphasis on patient-doctor relations) and “Film Is Evil, Radio Is Good” (the title was the theme) in 1987; then for “Pearls for Pigs” (about a mentally disturbed actor) and “Benita Canova” (about mean schoolgirls) in 1998. Some people count those as two Obies, others as four.

In between, Mr. Foreman received the best director award for Vaclav Havel’s “Largo Desolato” (1986) and a special Obie (1988) for sustained achievement.

In 1995, when he was 58, Mr. Foreman received a MacArthur Foundation fellowship, popularly known as the “genius grant.” The foundation praised him for his “original vision and commitment to developing new theatrical vocabularies” that influenced the direction of American avant-garde theater.

No one could credibly accuse Mr. Foreman of abandoning his bohemian roots and going mainstream, but he did direct and design numerous classical works and operas both in the United States and abroad. They included Johann Strauss’s “Die Fledermaus” at the Paris Opera, Mozart’s “Don Giovanni” at Opéra de Lille, France, Molière’s “Don Juan” at the Guthrie Theater in Minneapolis and Joseph Papp’s production of Kurt Weill and Bertolt Brecht’s “The Threepenny Opera” at Lincoln Center in New York.

Mr. Foreman was well-known in SoHo, where he bought a 3,600-square-foot loft for $10,000 in 1970. (“Now it’s all Boutiqueville,” he observed regretfully, referring to the neighborhood, in a 2013 Times interview.) Early in his career he was identifiable by his matching dark hair, eyebrows and walrus-style mustache. Decades later, when the mustache was gone and his hairline had receded, The Forward described him affectionately as “a disheveled, egg-shaped man with long, stringy hair and frayed, formless clothes.”

Suffering from light sensitivity, Mr. Foreman said, he usually rose well before dawn, covered the apartment’s skylights with fabric and went to bed around 7 p.m. He was a frequent napper. “I lie around, I doze off,” he told The Times. “It’s been a life of bits and pieces.”

It was a life of purpose as well. “I’ve never been very happy about the world,” he confessed in a 2018 video interview for the Lower East Side Biography Project. “So what makes me tick is this obsessive need to figure out what isn’t here that I want to be here. I make plays — or whatever you want to call them — to try to fill that great big void.”

Richard Foreman was born Edward Friedman on June 10, 1937, in Staten Island. He was adopted by Albert Foreman, a lawyer, and his wife, Claire (Levine) Foreman; the Foremans soon moved to Scarsdale, in Westchester County.

Richard graduated from Scarsdale High School, where he showed an early interest in theater, appearing in class productions. He also produced and directed Arthur Miller’s “The Crucible” there, just two years after the play’s 1953 opening on Broadway. He graduated in 1959 from Brown University, where he majored in English and helped form the student theater group there; he also sometimes designed sets. Three years later, he received an M.F.A. from the Yale School of Drama (now the David Geffen School of Drama at Yale).

His father helped him get his first job, managing apartment buildings in New York, Mr. Foreman said in the Biography Project interview. That gave him a flexible schedule and allowed him to pursue artistic projects. His father then helped him again, showing one of his early plays to someone at the influential Shubert organization, who encouraged him and introduced him to a producer.

Early on, Mr. Foreman became part of a downtown filmmaking group that included Jonas Mekas. With Mr. Mekas as his guru, he made film shorts in the 1970s, adapted his play “Strong Medicine” to film in 1981 and returned to movie production in 2012 with “Once Every Day” and a documentary about its making, “My Name Is Rainer Thompson and I’ve Lost It Completely.”

His last film was “Mad Love” (2018), a 70-minute reverie, mostly in grainy black and white, released by PennSound Cinema. Its central image was of a well-dressed man inserting his index finger into a well-dressed woman’s open mouth.

The last play he produced and directed himself was “Old-Fashioned Prostitutes (A True Romance),” which opened at the Public Theater in 2013. In a review of the play, which he called a “gleeful mind- and memory-bender” about an aging man watching the present “turn into the past,” Mr. Brantley praised Mr. Foreman as “the most eminent elder statesman of the avant-garde in New York theater.”

Mr. Foreman’s first play in a decade, “Suppose Beautiful Madeline Harvey,” about, on the surface, a woman and a man at a boulevard cafe, was staged in December at LaMaMa, the East Village experimental theater, and directed by Kara Feely.

Mr. Foreman married his high school friend Amy Taubin, an actress who became a New York film critic, in 1961; they divorced in 1972. In 1988, he married the artist and actress Kate Manheim, who has appeared in a number of his plays. She is his only immediate survivor.

In a 2013 essay in The Forward, Joshua Furst compared the power of Mr. Foreman’s work to the Jewish tradition of davening: “If you let the rhythm of his rocking enter you, he’ll remind you what it feels like to be ecstatic, what it is to be hysterical, what it means to circle the meaningless void that is the wellspring of all meaning.”

Michael Paulson contributed reporting.