Anyone who came to opera in the mid-1950s, as I did, knew Maria Callas, because unlike her contemporaries—but very much like Leonard Bernstein—she attracted media attention wherever she went. Lenny was on television and featured in New York reviews (mostly negative) and glamorous photo shoots, and Callas, who maintained a private and adoring press agent—the redoubtable Elsa Maxwell, who was also a gossip columnist—was seemingly always surrounded by scandal, controversy, conflicting critical assessments, and wild adoration.

As a boy, I knew what she looked like because there would be articles about her in popular magazines, like Life magazine. Edward R. Murrow interviewed her live in 1958 on his interview series, Person to Person. She performed a scene from Tosca on the popular variety program The Ed Sullivan Show. All other sopranos were somehow small compared to Callas. Her biggest rival, Renata Tebaldi, had the most enormous and warm soprano voice and was a tremendously empathetic presence onstage, but Callas dismissed her publicly when she was quoted in Time magazine saying that comparing her to Tebaldi was like “comparing champagne to Coca-Cola.”

Callas seemed always to be in the news, even as her voice—never beautiful—disintegrated before us. But that never stopped us from wanting more and more, and when she recorded the mezzo-soprano role of Carmen, the opera world thought she might have a new career as a mezzo-soprano, but this was not to be.

But before Carmen—and after Callas’s seven-year absence—Rudolf Bing, the general manager of the Metropolitan Opera, who had feuded with her publicly in 1958, announced that Madame Callas would return to the Metropolitan Opera House in Tosca. It would be difficult to describe the effect this announcement, made in the summer of 1964, had in New York. I, for one, had never seen her perform, and her life had been front-page tabloid news. On that night of her return—Friday, March 19, 1965—I sat in the Dress Circle at the Metropolitan Opera House and witnessed history.

Callas said that comparing her to Tebaldi was like “comparing champagne to Coca-Cola.”

The other two principals that night were Franco Corelli, the world’s most handsome tenor—who possessed a glorious and huge voice—and the greatest actor-baritone, Tito Gobbi, with whom Callas had recorded Tosca twice. Franco Zeffirelli provided Maria with new costumes, and on that night, we heard her voice, unamplified and unedited, making Tosca’s offstage vocal entrance, “Mario! Mario! Mario!”

The effect on the audience was something I have never experienced since that night. All the press and all the scandals (she had already left her husband to take up with one of society’s richest men, Aristotle Onassis), all the cancellations—the entire Callas mystique—coalesced because at that moment, she was there. She had not canceled. We were the chosen few thousand who would hear the greatest singing actress of the 20th century sing a signature role and no one—no one—outside of that theater would ever know what we were about to know. There was a general inhalation. It was as if someone down in the orchestra had put his finger into an electrical outlet and we were all holding hands.

Callas and Aristotle Onassis, who began their affair in 1959, get playful at the Lido in Paris, in 1966.

Before the performance had started there were people with placards marching around 39th Street and Broadway, where the “old Met” was situated, reading, Franco Corelli is the World’s Greatest Tenor, in case we were focusing too much of our attention on Callas. (I know. Hard to imagine today.) After Corelli had sung his opening aria, Maria entered, carrying dozens of yellow roses. For a small inkling of the moment of her entrance, a recording exists that is available on the Internet.

While the shouting and applause continued into a seeming infinity of emotions, Callas froze in Corelli’s arms. The music stopped. My opera glasses were fixed on her. I could see her emotional breathing, waiting, waiting for the orchestra to start again so she could return to character … And when she did, she was Tosca: a sexual diva with a vulnerability that made her and her artistry so precious.

Callas and Tito Gobbi make a first-act curtain call during Tosca in 1965.

Gobbi and Corelli were in splendid voice. Callas was doing whatever she could do to be Tosca. I remember, during the first intermission, looking down from the first row of the Dress Circle to see the gossip columnist Elsa Maxwell with Jacqueline Kennedy in one of the center boxes. Mrs. Kennedy was radiant. Her skin shone up toward me in the most startling way, and I only remembered the effect it had when I met Princess Diana many years later at La Scala. Diana had the same radiance.

It was as if someone down in the orchestra had put his finger into an electrical outlet and we were all holding hands.

Mrs. Kennedy, having emerged from more than a year of mourning the death of her husband, wore a powder-blue strapless Empire gown and long white opera gloves. Onstage, Maria Callas wore a deep-red velvet Empire gown. One was a serene royal observer and the other a passionate tigress. The common denominator was the multi-billionaire shipping magnate Aristotle Onassis, Mrs. Kennedy’s future husband and Miss Callas’s current paramour. Unknown to us at the time, however, was the other opera playing out that evening.

Jackie Kennedy, in her first outing since President Kennedy’s assassination, attends Callas’s return to New York City’s Metropolitan Opera in 1965 alongside its general manager, Rudolf Bing.

Callas’s Act II was her tour de force. When her beloved Mario was being tortured offstage and it was announced that he had fainted, she literally pounded the chest of the messenger, Sciarrone, with her line “Assassino!” (murderer). We laughed with joy. Yes, we laughed. And when Gobbi was writing the free passage for Tosca and her lover, and she was desperate to escape what would be a rape, Gobbi took his quill—Callas was downstage of the desk—and provocatively brushed it against her naked arm. Callas, in a fury, grabbed for it, just missing it as Gobbi continued his writing.

I remember wondering how Gobbi’s Scarpia would avoid being upstaged by Callas’s Tosca once he was dead. As it turned out, he knew exactly what to do: he died with his eyes opened. My opera glasses were fixed on him, and he never seemed to blink as Callas placed the candles at his side and dropped the crucifix on his chest. She could have jumped on his chest and we would not have noticed. He just stared into the house and did not blink.

In Act III, Tosca explains to her lover how she stabbed Baron Scarpia. The words “Io quella lama gli piantai nel cor” (That pointed blade I planted in his heart) required Callas to sing a high C. That is when she lost us. The note was horrific.

I remember that I looked up at the Met’s chandelier to see if it was still secure after the sound she made. I sadly thought all that we had hoped for and that she had achieved was now destroyed.

Mrs. Kennedy, having emerged from a year of mourning the death of her husband, wore a powder-blue strapless Empire gown and long white opera gloves.

But she managed the ending, which is not vocally difficult, and she could depend on Corelli’s strength to support her in their final duet. And when she committed suicide by leaping off the parapet, she did exactly what the libretto says: she hurled herself by jumping up in the air, tumbling out of sight of those of us who were once again spellbound by her performance.

Years earlier, when I was just a teenager, I had written to every artist in the Metropolitan Opera for what was known as an “8-by-10 glossy.” This is a black-and-white professional photograph used for publicity, and the old Met would display these pictures on the wall of the lobby that surrounded the ticket booths. I could not resist writing Callas and asking for an autographed photo. And to my amazement, she actually sent me one.

Callas takes a solo bow at the Metropolitan Opera after singing Tosca on March 19, 1965.

But Callas had a way of giving and immediately taking away. In an interview about the enormous success of her return to New York, she thanked her fans and added, “Of course, it’s the ones who don’t ask for anything but my art that I most value.”

When Leonard Bernstein went to Harvard to deliver his Norton Lectures, in 1973, he decided to include Igor Stravinsky’s opera-oratorio, Oedipus Rex, as part of the series. Not only would he speak of it, but he would also perform it with the Boston Symphony Orchestra, record it, and videotape it. I was with him when he developed a wish list of cast members that included Sir Laurence Olivier for the role of the narrator—and Maria Callas to sing the role of Jocasta.

Lenny had, of course, a significant history with Callas, having made his La Scala debut conducting her in Cherubini’s mostly unknown opera Medea in 1953. He did a devastating imitation of her and her “New Yawk” accent—something she subsequently lost. “Except for an elementary-school teacher, she is the only person to call me ‘Lennid.’”

That is when she lost us. The note was horrific.

And so, Bernstein called Callas in Paris. He recounted his “pitch” to me a few weeks later, how he attempted to cajole her out of retirement. He told her that Jocasta was the perfect vehicle for her return because the role never went above a G (a good deal lower than the high C that practically had done her in when she was still singing Tosca). The text was in Latin, which meant that no one would be comparing it to any role she had ever done before. Since it was an opera-oratorio, there would be no staging, and therefore it would not take up too much time. Jocasta sings only one aria and a duet with her son, Oedipus. Jocasta is the only woman in the cast.

I remember this pitch because of what happened when Lenny called for her reply. She said that she had also been considering performing Beethoven’s Ninth Symphony, something that Bernstein scoffed at. (“I cannot imagine Maria has ever heard it,” he said.) She then explained why she was declining his offer.

“First of all, it only goes up to a G, and I am a soprano. Second, it is in Latin, a language I have never sung in. Third, I am a theatrical artist, and singing a role that is not staged is not of interest. Fourth, it was only one aria and a duet. Fifth, I am uncomfortable performing in a work that had only one woman in it.” Every reason he had given her to sing the role was used as her reason not to sing the role.

Callas congratulates Leonard Bernstein following a performance of “Homage to Ravel” with the Orchestre National de France, which he conducted in 1975.

Thus, I began to understand just how complicated it must have been to be Maria Callas—frightened, alone, and imperious. That every singer must learn to die twice was something the American soprano Phyllis Curtin often told students. The role ultimately went to Tatiana Troyanos, and the narrator’s role was taken by Lenny’s friend the actor and voice-over artist Michael “Mendy” Wager—who provided the “voice” of PBS as well as for Liquid Drano (“Madame, do your sinks clog up at night?”).

Two years before her death, in 1977, I met Maria Callas. She had come to see Leonard Bernstein conduct a concert with the Orchestre National de France, for which I had prepared the musicians. Callas came backstage during intermission, dressed in dark green, her auburn hair piled high, and her capped teeth exaggerating her smile. She arrived to tell Bernstein that she had a terrible headache and was going home. Bernstein protested, but Callas was adamant. That’s when he said, “This is my assistant, John Mauceri.” She took one look at me, decided I was worthless, and said her good-bye to “Leonard.”

And that’s when and where Leonard Bernstein and Maria Callas last saw each other, and the night I met Maria Callas.

John Mauceri is the author of The War on Music—Reclaiming the Twentieth Century (Yale University Press) and was the musical adviser to the Todd Field film Tár, starring Cate Blanchett