In October 1967, Joseph Papp’s Public Theater opened with the world premiere of “HAIR: The American Tribal Love-Rock Musical.” It didn’t yet include the famous nude scene — that would be added for the Broadway production, which opened in 1968 — but it was already something different: a rock musical, set in the present, about the kids who were turning on and dropping out, hanging out in the East Village and protesting the Vietnam War in Central Park.

The show aroused strong reactions. Some people were offended by the four-letter words and what they saw as desecration of the American flag in the song “Don’t Put It Down.” Two cases involving the show went to the Supreme Court, and in some cities where it toured, there were bomb threats against the theater. Others loved it.

“We felt like we were changing the world one audience at a time,” said Jonathan Johnson, who was in several early productions and is the author of the book “Good HAIR Days: A Personal Journey with the American Tribal Love-Rock Musical.”

It’s unlikely that the Public’s 40th anniversary concert next weekend, which will include young Broadway stars like Jonathan Groff (“Spring Awakening”) and Karen Olivo (“In the Heights”), will produce any such divided responses. But the songs are still infectious (as their frequent use in movies and television ads demonstrates), and the picture of the 1960s counterculture still compelling. Interviews with people involved in the original Public Theater and Broadway productions illustrate that the story behind “HAIR” is just as wild as the story onstage, in part because two of its three creators, Gerome Ragni and James Rado, originated the lead roles of Berger and Claude and put much of themselves into them.

Ragni and Mr. Rado were close friends who were fascinated by the hippie culture they saw developing around them. Both were actors — Ragni (who died of cancer in 1991) was from Pittsburgh, Mr. Rado from D.C. — and they met in an Off-Broadway show in 1964. They wanted to write a musical and decided their subject should be the youth culture.

“There was so much excitement in the streets and the parks and the hippie areas, and we thought if we could transmit this excitement to the stage it would be wonderful,” he recalled in an interview. “We hung out with them and went to their Be-Ins [and] let our hair grow,” Mr. Rado said of the hippies. At the antiwar marches, “[w]e were caught up in the emotionalism of the scene, but we’d be taking notes at the same time, of what the posters said, and what the chants were.”

Walter Michael Harris, who would become the youngest member of the original Broadway cast at 16, and whose family lived in the East Village, said his mother remembered Ragni pushing a baby carriage around the neighborhood, filled with notes on scraps of paper.

“He would stop people and pull out a paper bag with some lyrics on it, and ask them what they thought,” Mr. Harris said.

An early producer connected Ragni and Mr. Rado with the composer Galt MacDermot, who had recently moved down from Canada. At the time, Mr. MacDermot said, he was not involved in the counterculture. “I had short hair, a wife, and, at that point, four children, and I lived on Staten Island,” he said.

After shopping the show around to Broadway producers with no success, Ragni ran into Papp on a train from New Haven to New York and handed him the script. A few days later, Ragni, Mr. Rado, and Mr. Mac-Dermot went to Papp’s office at the Public Theater, which was still under construction, and played and sang the score for him. Papp decided to open his new theater with a sixweek run of “HAIR.”

Although the show was a success at the Public, “[w]e always intended it for the uptown audience,” who weren’t already sympathetic to the hippie movement, Mr. Rado said. “We wanted to open hearts to peace.”

Michael Butler was a wealthy young man from Oak Brook, Ill., who had recently been turned on by a local kid who was taking care of his garden (and growing marijuana in it). He was planning a run for Senate on an antiwar platform when he made a trip to New York and saw, at his racquet club, the poster for “HAIR: The American Tribal Love-Rock Musical.”

“I thought it was an Indian show, and I had always been very concerned about Indian problems,” Mr. Butler said in an interview, so he decided to see it. When he went to a preview and discovered it was, instead, an antiwar musical, “I thought this would be a great thing to take to Illinois and have my constituency see.” Papp wasn’t interested in sending the show to Illinois, but later he called Mr. Butler and asked if he wanted to do a coproduction, which went up at the Cheetah, a discothèque on Broadway.

At the Cheetah, the show had to begin early and run without intermission so the club could open in time for the dance crowds. The run was not a success, but Mr. Butler acquired the rights and took the show to the Biltmore Theatre. He brought in Tom O’Horgan — whom Ragni and Mr. Rado knew from his work downtown at La Mama — to direct. On Broadway, it was a hit and ran for four years — and probably would have run longer, Mr. Butler said, if they hadn’t at the same time opened productions all over the country, from Boston to San Francisco to Los Angeles to Miami, and then all over the world.

Some people in the Broadway production went on to major acting careers: Diane Keaton, for instance. Shelley Plimpton and Keith Carradine met in the Broadway production and conceived their daughter, the actress Martha Plimpton. (The younger Ms. Plimpton played Helena in the production of “A Midsummer Night’s Dream” that closed last weekend at the Delacorte.)

But many more were nonprofessionals whom the casting director found hanging out on St. Mark’s Place. Daniel Sullivan, now a highly sought-after director (who directed the just-closed “Midsummer Night’s Dream”), came on as an assistant stage manager in the midst of the Broadway run, during what he described as “fairly turbulent times” for the production.

“At least four or five kids would not show up” each night, he said. “You had to recast those roles, and since each kid played 30 or so roles over the course of the evening, you had to know what all their vocal ranges were, and then 10 minutes before the show announce who would be playing what parts.”

Ragni and Mr. Rado eventually turned over their roles to others, but Mr. Butler said he thought the power of the story came from its being “very autobiographical” on their parts. Early on in the show, Ragni separated from his wife — though he never divorced her, possibly because he was fervently, if conflictedly, Catholic. He and Mr. Rado were very close, and several people interviewed for this article said they assumed that the men were in a romantic relationship. If so, it was a stormy and volatile one. By the time they left “HAIR,” “[w]e couldn’t be in a room together, we would burst into an argument,” Mr. Rado said. They worked on separate projects for a while, but after a year or so, they got back together and wrote another show, “Sun,” about the environment.

People interviewed for this article described Ragni as charismatic and impulsive and Mr. Rado as quieter and more cerebral. Ragni’s son, Erick, who is now an architect in Houston, said he remembered his father and Mr. Rado (sometimes referred to as “Dad number two”) going to the YMCA on 23rd Street. His father would be upstairs, manically lifting weights, and “Jim would be down in the mat room, meditating. That was the difference between them.”

Erick lived with his mother but would visit his father in the city and has fond memories of “HAIR.” (He is coming to New York to see the concert next weekend.) Of his father, he said, “He was a kind of free spirit. He would just take off sometimes. One time he just disappeared for a few months, and his sisters were really worried. They sent these private investigators and they found him at the Meridien hotel in Rio de Janeiro, hanging out at the pool.”

The wealth that “HAIR” brought didn’t change his father at all, he said. In fact, he said, he thought his father’s “most successful theater ventures” took place in his everyday life. At fancy restaurants, “he’d have markers and do these gigantic drawings all over the tablecloth,” Erick said. He enjoyed “challenging everyone’s preconceived limits of what they thought was proper or not, and acceptable or not,” he added.

Asked if his father would have been gay if he hadn’t been strongly Catholic, he said his father’s private life was “very complex. I think he had relationships with men and relationships with women.”

Mr. Rado, who has never married, said he did not identify as gay. Asked if the story of “HAIR” was based on his and Ragni’s relationship, Mr. Rado said yes. “This very strong love friendship — I think everything came out of that, really,” he said. “We were in a love mode, and this whole love movement started happening around us, so the show got it,” he continued. “‘HAIR’ was our baby in a way, which is pretty cool.”