The comedian is starring in “Mr. Saturday Night,” a musical version of his 1992 movie about an aging performer who won’t accept that his time in the spotlight is up.“The worst nightmare is, do you wake up one day and you’re not funny anymore?” Billy Crystal, 74, said of the anxiety that comes with being an aging comedian. “Do you wake up and you’re not relevant?”Philip Montgomery for The New York TimesA funny thing happened in the rehearsal room of “Mr. Saturday Night” a few weeks ago. Billy Crystal was performing a scene from this new Broadway musical in which his lead character, an aging, out-of-touch comedian named Buddy Young Jr., has learned that he was mistakenly included in an in memoriam segment on the Emmy Awards.Invited to appear on the “Today” Show to correct the error, Buddy sees an opportunity to reclaim the spotlight he once commanded. With that motivation, Crystal turned to his co-star David Paymer, who plays Buddy’s endlessly loyal brother, Stan, and he began to sing a song about his deep yearning for a crowd’s attention:What I was, way back thenI could have that back againI could be — still could beThat guyIt’s an essentially comedic song, delivered in the warm, warbling voice we heard Crystal employ each year when he was a ubiquitous comedy star and a reliably genial Academy Awards host.“Mr. Saturday Night,” which opens April 27 at the Nederlander Theater, is a throwback to the era of Crystal’s hegemony in the 1980s and early ’90s, when he straddled the cultural landscape with his standup specials and hit films like “City Slickers” and “When Harry Met Sally…”Crystal as the out-of-touch comedian Buddy Young Jr. (who is mistakenly included in an awards show’s in memoriam segment) and Randy Graff as Buddy’s wife, Elaine, in the new musical.Sara Krulwich/The New York TimesThe film version of “Mr. Saturday Night,” which Crystal starred in and directed in 1992, felt like a strange misstep at the time. Far from the eager rib-ticklers he was known for, Crystal — then 44, under layers of old-age makeup — played Buddy as a selfish curmudgeon who has alienated his family and refuses to accept that his career is over.Now 74, Crystal is not that guy — if he doesn’t enjoy the outsize dominance he once had, he doesn’t share Buddy’s desperation to reclaim it, either.Still, as Crystal told me a few days before the rehearsal, there is a certain pleasure he finds in revisiting this singularly disagreeable character: “To play him 30 years later, they actually have to make me younger,” he joked.But seriously, folks: Crystal explained that when he performs as Buddy in the stage musical, he isn’t weighed down by elaborate prosthetics or an aura of likability, and it brings a newfound ease to his performance.“When he’s cantankerous and edgy with people, it’s in front of a live audience,” he said excitedly. “I feel them get upset with him and I hear them go, ‘Ooh.’”Having lived long enough to match the character in age and to experience the kinds of setbacks and regrets that shaped him, Crystal understands that Buddy is not a bad guy. “He’s misunderstood and confused, bitter and regretful, and time is running out,” he said.This is the point where Billy Crystal and Buddy Young Jr. really intersect: at the realization that there is more life behind them than in front of them, and the anxiety that they might never again be as good as they once were.For himself, and for any comedian who cares about the art, Crystal said, “The worst nightmare is, do you wake up one day and you’re not funny anymore? Do you wake up and you’re not relevant? When does that happen?”He added: “There’s a magic about when it’s good, and when it’s bad, it’s really something incredible. There’s a terrible feeling of, I’m losing them.”“It’s not an Ahab thing — it’s not his white whale,” the screenwriter Lowell Ganz said of why Crystal is revisiting “Mr. Saturday Night.” “He has a real affection for the character because he loved those guys.”Philip Montgomery for The New York TimesNot that Crystal lets this fear keep him up at night — “I’m a bad sleeper, anyway,” he said. “I don’t need to worry about more than I’m worrying about” — but the best solution he has found is to focus on projects that put him to the test, like “Mr. Saturday Night.”“You’ve got to keep pushing ahead and not let anybody leave you behind,” he said.In early March, I met with Crystal at his spacious penthouse apartment in downtown Manhattan. Dressed in a long-sleeved T-shirt, jeans and sneakers, he was a subdued but still quippy host as he showed off some of his artifacts: a desk nameplate for Dr. Benjamin Sobel, his “Analyze This” character; an enlarged photograph of celebrity guests at the 1937 Oscars. (“Even then, the show ran too long,” he said.)Crystal’s love of nostalgia and showbiz history helped inspire the character of Buddy Young Jr., a Don Rickles-like insult comic he played in segments on HBO specials and “Saturday Night Live” before giving him a full life in “Mr. Saturday Night.”That film, which he wrote with the “City Slickers” screenwriters, Lowell Ganz and Babaloo Mandel, was Crystal’s feature-directing debut. Back then, becoming the wizened entertainer required five hours a day to put his old-age makeup on and another two hours to take it off: “They’d cut a hole in my bald cap and you’d hear, whooooosh,” Crystal recalled. “It was like Jiffy Pop.”Paymer, who also played Stan in the film, received an Oscar nomination. But the movie was a commercial dud, grossing just $13 million domestically. (“City Slickers,” by comparison, made $124 million.) “It was the biggest disappointment that it didn’t do well,” Crystal said.His film collaborators said that Crystal was especially stung by the failure because he had intended “Mr. Saturday Night” as a tribute to the tenacious golden-age comedians he grew up admiring.“It’s not an Ahab thing — it’s not his white whale, and I don’t think he deals in that kind of neurosis,” Ganz said. “But he has a real affection for the character because he loved those guys.”In the years after “Mr. Saturday Night” was released, Crystal entered a foreseeable cycle of hits and misses. (“Analyze This,” yes; “City Slickers II: The Legend of Curly’s Gold,” no thank you.)This is Crystal’s first Broadway musical (he took voice lessons during the pandemic lockdown). His previous Broadway outing, the autobiographical one-man show, “700 Sundays,” won a Tony Award in 2005.Philip Montgomery for The New York TimesHe had seemingly hosted his last Oscars in 2004, until he got called in to pinch-hit in 2012 — an act meant to bring some dignity back to the show after its co-producer Brett Ratner resigned after making offensive public remarks and his chosen M.C., Eddie Murphy, exited after him.Rather than coast to his own emeritus status, Crystal has lately appeared in projects that have paired him with younger stars: the short-lived FX series “The Comedians” with Josh Gad; modest existential comedy-dramas like “Standing Up, Falling Down” with Ben Schwartz; and “Here Today” with Tiffany Haddish.He remained on the lookout for new projects to engage him. In 2017, he toured with the actress Bonnie Hunt, at appearances where she interviewed him about his life and career. Though he was planning to shape this material into a new show, Crystal said he backed off the idea: “One word came to my mind that pulled me away from it — easy. It’s not a challenge.”He had already starred in his autobiographical one-man show, “700 Sundays,” whose original Broadway run won a Tony Award in 2005. At that time, he said Mel Brooks had approached him about being a replacement cast member in his musical “The Producers.” (As Crystal recounted the story, “I said, ‘Do I really want to be the eighth guy to play Max Bialystock?’ He said, ‘You won’t be — you’ll be the 12th.’”)Crystal in the 1992 movie.Entertainment Pictures/AlamyBrooks also raised the suggestion of a “Mr. Saturday Night” musical, which Crystal said he’d do only if Brooks starred in it. (A representative for Brooks’s production company confirmed their conversation.) This casting didn’t come to pass either, but Crystal continued to reflect on the idea for another decade.Around 2015, Crystal said he got serious about the musical. At that point, when he contemplated playing Buddy Young Jr., he said, “It’s easier.”By then, he’d also become more familiar with the whiplash oscillations of show business that were mostly speculative when he made the movie. “I’ve had ups and downs and sideways and middles, and the middles may be harder than the downs,” he said. “The middle, that’s the weird one, because you’re looking up and looking down at the same time.”Crystal, Ganz and Mandel wrote a new book for the musical, one that charts Buddy’s trajectory from Catskills dining-room cutup to TV star to washout, and the show features songs with music by Jason Robert Brown (“Parade,” “The Bridges of Madison County”) and lyrics by Amanda Green (“Hands on a Hard Body”).Its director, John Rando (“Urinetown,” “The Wedding Singer”), said that where the film used younger performers to flash back to Buddy’s earlier days, the actors in the musical will play their characters at every age. In his initial conversations with Crystal, Rando recalled, “I said I want to see Billy Crystal play his 20-year-old self and his 40-year-old self and his 70-year-old self. This is the theater and we should capitalize on that.”In workshopping the musical, Rando said that the overall size of the cast shrank from about 20 people to a more intimate group of eight. “That made us discover the real heart and pulse of the show, which is Buddy’s family, and how each of them relate to him,” he said. (The principal Broadway cast also stars Randy Graff as Buddy’s wife, Elaine, and Shoshana Bean as his estranged daughter, Susan.)But just as “Mr. Saturday Night” was nearly ready to go before audiences, the onset of the pandemic in March 2020 halted work on the show. Crystal hunkered down with his family in Los Angeles, finding that his quarantine at least provided the time to focus on other writing projects. “It gave me a discipline.”For Crystal, who hasn’t performed in a full-length musical since 1981 (when he played the master of ceremonies in a Kenley Players production of “Cabaret” in Ohio), this was also a period he spent working with a vocal coach and practicing his songs.When “Mr. Saturday Night” was at last able to have an out-of-town tryout at Barrington Stage Company in Pittsfield, Mass., this past October, anxieties were running high. After hearing the audience clap and cheer for the show’s first performance, Crystal said he found Rando backstage and collapsed into his arms, crying with relief.“I felt like Dr. Frankenstein — it’s alive!” Crystal excitedly recounted. “We had a show.”Crystal on the set of the musical, which is in previews at the Nederlander Theater. Opening night is scheduled for April 27.Philip Montgomery for The New York TimesCrystal remained a persistent presence through the Broadway rehearsals at Pearl Studios in Midtown Manhattan, sometimes wandering its narrow room to joke around with his cast and stoke morale, but always watching fastidiously for opportunities to make refinements.“He’s more serious than I thought he would be,” said Bean, who has previously starred in musicals like “Hairspray” and “Waitress.”“If it’s a scene that he’s not involved in, he does listen in,” she said. “He stands there with his little arms folded and he squints his eyes and he’s paying attention.”Bean added, “I live for the moments when I can get him to crack a smile or laugh. It’s like the sun comes shining through on you for two seconds. And I don’t know if he’s just being polite or if he really thinks that I have charm, but it’s the greatest.”Paymer, who has now performed “Mr. Saturday Night” onscreen and stage, said that Crystal is constantly striving to find ways to reinvent the musical and keep it distinct from the film.“I said to him last week, ‘Well, in the movie, we did this,’” he recalled. “And he said, ‘Well, that was the movie.’ That, to me, was freeing. I found myself giving the same line readings at times. And then I stopped myself from doing that — don’t go back to the movie and say things exactly the way you did then.”However long “Mr. Saturday Night” runs, Crystal said that the physical and psychic demands of the show are exactly what he is looking for at this point in his life — a self-explanatory rebuttal to any potential argument that he’s running out of steam or should be looking to pack it in.“If you just do the math, you could say, all right, there’s less time to do stuff,” he said. “But why look at it that way?” Though there’s no established path for a comedian to follow at this point in his career, Crystal added, “the exciting thing about it to me is that there is no road map.”And making this incarnation of “Mr. Saturday Night” has taught Crystal that there is still so much more he wants to make, if he can just pace himself.As he explained, in a voice that was familiar for both its shticky-ness and its sincerity, “I have too much to do and I’m in no rush. When you rush, you make mistakes. That’s the old excuse: ‘How’d you fall?’ ‘I was rushing when I shouldn’t have rushed. I didn’t read the thing. I tripped and I fell.’ So, I’m just going to take it as it comes.” More