Working with his fellow writer and actor Gerome Ragni and the composer Galt MacDermot, he jolted Broadway into the Age of Aquarius.James Rado, who jolted Broadway into the Age of Aquarius as a co-creator of “Hair,” the show, billed as an “American tribal love-rock musical,” that transfigured musical theater tradition with radical ’60s iconoclasm and rock ’n’ roll, died on Tuesday in Manhattan. He was 90.The publicist Merle Frimark, a longtime friend, said the cause of his death, in a hospital, was cardio-respiratory arrest.So much of the power of “Hair” resided in its seeming raw spontaneity, yet Mr. Rado (pronounced RAY-doe) labored over it for years with his collaborator Gerome Ragni to perfect that affect. Contrary to theatrical lore, he and Mr. Ragni were not out-of-work actors who wrote “Hair” to generate roles they could themselves play, but rather New York stage regulars with growing résumés.They met as cast members in an Off Broadway revue called “Hang Down Your Head and Die,” a London transfer that closed after one performance in October 1964. Mr. Rado bonded with Mr. Ragni and was soon talking to him about collaborating on a musical that would capture the exuberant, increasingly anti-establishment youth culture rising all around them in the streets of Lower Manhattan — a musical about hippies before hippies had a name.A musician before he’d become an actor, Mr. Rado began writing songs with Mr. Ragni, which they sometimes sang in what were then beatnik coffee houses in Greenwich Village.Moving to an apartment in Hoboken, N.J., where rents were even cheaper than in downtown Manhattan, they borrowed a typewriter from their landlord and went to work writing their musical in earnest, transcribing into song the sexual liberation, racial integration, pharmacological experimentation and opposition to the escalating Vietnam War that was galvanizing their young street archetypes. In solidarity, Mr. Rado and Mr. Ragni let their short hair grow long.A museum stroll in mid-1965 brought them face to face with a painting of a tuft of hair by the Pop artist Jim Dine. Its title was “Hair.”“I called it to Jerry’s attention, and we were both knocked out,” Mr. Rado later recalled. Their nascent musical now had a name.A moment from the original production of “Hair,” at the Public Theater in Manhattan in 1967.DagmarWhat happened next would become the stuff of Broadway legend, albeit in fits and starts. In October 1966, on a train platform in New Haven, Conn., Mr. Ragni recognized Joseph Papp, impresario of the then-itinerant New York Shakespeare Festival, and handed him a bound script of “Hair.” Mr. Papp took it, read it and resolved to consider making “Hair” the opening production at his Public Theater, just nearing completion in what had been the old Astor Library on Lafayette Street in the East Village.Mr. Rado and Mr. Ragni, meanwhile, had decided that their lyrics needed better melodies than the ones they had written, and embarked on a search for a legitimate composer to improve the songs. The search yielded the Canadian-born Galt MacDermot, a most unlikely choice: He was slightly older than his colleagues and a straight arrow with an eclectic musical background but scant Broadway experience. Mr. MacDermot wrote the melody for versions of “Aquarius” and several other songs, on spec, in less than 36 hours. It instantly became clear that he was the ideal choice for setting Mr. Rado and Mr. Ragni’s lyric ruminations to rocking show music.A demonstration soon ensued in Mr. Papp’s office, with Mr. MacDermot singing and playing the trio’s new songs. Impressed, Mr. Papp announced that he would open the Public with “Hair.”Yet, second-guessing himself, he soon rescinded his offer, only to reconsider after a return office audition, this time with Mr. Rado and Mr. Ragni doing the singing. “Hair” did, in fact, open the Public Theater on Oct. 17, 1967, with the 32-year-old Mr. Ragni leading the cast as George Berger — a hippie tribe’s nominal leader — but without the 35-year-old Mr. Rado, who was deemed too old by the show’s director, Gerald Freedman, to play the doomed protagonist, Claude Hooper Bukowski, even though the character was based almost entirely on Mr. Rado himself.“Hair” — an impressionistic near-fairy tale of a flock of flower children on the streets of New York taking LSD, burning draft cards, shocking tourists and making love before losing their conflicted comrade, Claude, to the Vietnam War — ran for eight weeks at the Public’s brand-new Anspacher Theater, generating ecstatic word of mouth and reviews that ranged from perplexed to appreciative.A wealthy young Midwesterner with political ambitions and strong antiwar politics named Michael Butler stepped in to move the show, first to Cheetah, a nightclub on West 53rd Street, and then — much rewritten by Mr. Rado and his collaborators, and with a visionary new director, Tom O’Horgan, now in charge — on to Broadway, where Mr. Rado was restored to the cast as Claude.Mr. Rado, second from left, with, from left, the actor Paul Nicholas, Mr. Ragni, the actor Oliver Tobias and the director Tom O’Horgan in London shortly after “Hair” opened there in 1968.Getty“Hair” was a Broadway sensation, hailed for its irresistible rock- and soul-driven score, its young cast of utter unknowns, its often-searing topicality and its must-see 20-second nude scene. It ran for 1,750 performances after opening at the Biltmore Theatre, on West 47th Street, on April 29, 1968. (It is now the Samuel J. Friedman Theater.)“Hair” quickly conquered the culture at large — though there were naysayers, who found its nudity, flagrant four-letter words and flouting of the American flag objectionable. It played all across America and ultimately the world, engendering a 1979 film adaptation directed by Milos Forman — which was disavowed by Mr. Rado — and a Tony Award-winning Broadway revival in 2009 that Mr. Rado helped guide. The original cast album won a Grammy Award and was the No. 1 album in the country for 13 straight weeks in 1969. (It was inducted into the National Recording Registry of the Library of Congress in 2019.)The score generated ubiquitous cover versions. In 1969 alone, the Fifth Dimension’s medley of “Aquarius” and “Let the Sunshine In” reached No. 1 on the Billboard Hot 100 (it went on to win the Grammy Award for record of the year), while the Cowsills’ version of the title song reached No. 2, Oliver’s “Good Morning Starshine” hit No. 3 and Three Dog Night’s “Easy to Be Hard” got as high as No. 4. Among the many others who recorded songs from the “Hair” score was Nina Simone.“From the start, I envisioned that the score of ‘Hair’ would be something new for Broadway,” Mr. Rado later reflected, “a kind of pop-rock/show tune hybrid.”“We did have the desire to make something wonderful and spectacular for the moment,” he added. “We thought we’d stumbled on a great idea, and something that potentially could be a hit on Broadway, never thinking of the distant future.”James Alexander Radomski was born on Jan. 23, 1932, in Los Angeles to Alexander and Blanche (Bukowski) Radomski. His father was a sociologist who taught at the University of Rochester in upstate New York. Mr. Rado grew up in a Rochester suburb, Irondequoit, and then in Washington. He graduated from the University of Maryland, where he majored in speech and drama. A lover of Broadway musicals since childhood, he began writing songs in college and co-wrote two musicals that were produced on campus, “Interlude” and “Interlude II.”After serving two years in the Navy, he returned to pursue graduate theater studies at the Catholic University of America in Washington, writing both music and lyrics for a revue there called “Cross Your Fingers.” After moving to New York, he wrote pop songs; recorded with his band, James Alexander and the Argyles; performed in summer stock; and did office work while studying method acting with Lee Strasberg.He landed his first Broadway job in 1963 in the ensemble of “Marathon ’33,” written by the actress June Havoc and produced by the Actors Studio. Following their initial encounter in 1964, he and Mr. Ragni were cast by Mike Nichols in his 1965 Chicago production of Ann Jellicoe’s comedy “The Knack.”In 1966, Mr. Rado appeared on Broadway in James Goldman’s “The Lion in Winter,” originating the role of Richard Lionheart, the oldest son of Henry II of England. His mainstream theatrical focus, however, was being redirected to the downtown avant-garde by Mr. Ragni, who, through his involvement with the Open Theater and Ellen Stewart’s La MaMa E.T.C., introduced Mr. Rado to the experimental aesthetic that became central to the experience of “Hair” onstage.“The truth is, we unlocked each other,” Mr. Rado wrote in a foreword to the book “Hair: The Story of the Show That Defined a Generation” (2010), by Eric Grode. “He was my creative catalyst, I probably his. We were great friends. It was a passionate kind of relationship that we directed into creativity, into writing, into creating this piece. We put the drama between us onstage.”Mr. Rado in 2017 at a Jazz at Lincoln Center celebration of the 50th anniversary of the Off Broadway opening of “Hair.”Krista Schlueter for The New York TimesIn the immediate aftermath of “Hair,” Mr. Rado’s fellowship with Mr. Ragni fractured. “We couldn’t be in a room together, we would burst into an argument,” he recalled. Mr. Rado wrote the music, lyrics and book (with his brother, Ted) for a “Hair” sequel he called “The Rainbow Rainbeam Radio Roadshow,” which ran Off Broadway in 1972, just as Mr. Ragni and Mr. MacDermot were suffering an ignominious Broadway flop with their post-“Hair” musical, “Dude.” Mr. Rado then reunited with Mr. Ragni to write “Sun (Audio Movie),” an environmental musical, with the composer Steve Margoshes, and “Jack Sound and His Dog Star Blowing His Final Trumpet on the Day of Doom,” also with Mr. Margoshes.Mr. Ragni died in 1991. Mr. MacDermot died in 2018.In 2008, Mr. Rado confirmed in an interview with The Advocate what had long been an open secret among his “Hair” castmates and collaborators: that he and Mr. Ragni had been lovers.“It was a deep, lifelong friendship and a love of my life,” Mr. Rado stated simply. “Looking back,” he later elaborated about “Hair,” “what was really underlying the whole thing was the new way men were relating to each other. They were very openly embracing each other as brothers. It wasn’t gay; it wasn’t repressed… We suddenly realized this was a musical about love in the larger sense.”Mr. Rado, whose brother is his only immediate survivor, never married and did not identify as gay, but rather as “omnisexual.” Asked before the 2009 “Hair” revival opened if the show was based on his relationship with Mr. Ragni, Mr. Rado answered yes.“We were in a love mode,” he said, “and this whole love movement started happening around us, so the show got it. ‘Hair’ was our baby in a way, which is pretty cool.”Maia Coleman contributed reporting. More