Decades before Dr. Anthony S. Fauci became a household name during the coronavirus pandemic, one of his detractors wrote that he was “a murderer” and “a liar” who “should be put before a firing squad.”

The man behind those words was Larry Kramer, the argumentative writer and activist who helped shape the modern gay rights movement during the AIDS crisis and who died in May 2020 at 84.

On Monday evening, at a memorial for Mr. Kramer at the Lucille Lortel Theater in the West Village, Dr. Fauci was among the speakers. The second he strode onto the stage, people applauded.

In his speech, Dr. Fauci described his long, complicated relationship with Mr. Kramer, starting with the fiery words that appeared in the The San Francisco Examiner in 1988, when he was four years into his nearly four-decade tenure as the director of the National Institute of Allergy and Infectious Diseases. At the time, Mr. Kramer blamed Dr. Fauci for the Reagan administration’s tepid response to a disease that had claimed tens of thousands of lives in the United States by then.

The two men went on to have a deep relationship — a long, intricate dance that concluded in May 2020 with a brief conversation. As Dr. Fauci described it from the stage, Mr. Kramer whispered, “I love you, Tony,” and Dr. Fauci replied, holding back tears, “I love you, too.”

Even after they began getting to know each other, Mr. Kramer did not let up on the criticism. At one point he castigated Dr. Fauci for refusing to chain himself to the White House fence in protest of the government’s handling of the AIDS epidemic.

“I explained to him that this would be 15 minutes of attention, and I would then immediately lose all access to the White House,” Dr. Fauci said. “No matter. He still felt I should do it.”

Not long after that disagreement, Mr. Kramer invited Dr. Fauci and his wife, Christine Fauci, to the New York opening of his play “The Destiny of Me.”

“Right here at this very theater,” Dr. Fauci said.

The play is a barely fictionalized version of his life during the AIDS epidemic. One of its characters is a cowardly doctor named Anthony Della Vida. Dr. Fauci said he was well aware that he was the basis for the character — knew that he had been, as he put it, “trashed.” But he also saw humanity in the portrayal.

“At the end,” Dr. Fauci said, “Larry rushed toward me in the back and asked apologetically, ‘Are you pissed off at me?’ I told him the play was masterful and that I was not offended at all.”

Well, no one ever listed among Dr. Fauci’s faults an inability to deal with combustible personalities. And in this case, his ability to forgive came partly from his awareness that Mr. Kramer was engaged in a form of role play, honing the tools he had developed as a screenwriter in Hollywood (his script for the 1969 adaptation of “Women in Love” by D.H. Lawrence was nominated for an Oscar) and then as a playwright.

Those tools resulted in his becoming, in Dr. Fauci’s estimation, “the driving force” who “crashed down” the wall separating patients from the medical establishment.

Mr. Kramer’s actions were marked by “confrontation, outrageous behavior and insults,” Dr. Fauci said, but they were followed by “insights, rationality, sensitivity, vulnerability, empathy and even humor.” In his view, Mr. Kramer’s “outrageous behavior” was the product of an “unselfish goal” related to “the plight of his people.”

The force of Mr. Kramer’s personality came through in a highlight reel of his speeches and TV appearances that was shown at the start of the memorial. One of his pet peeves was the word “epidemic,” which he felt allowed for a jargon-y obfuscation of the AIDS crisis.

“Why can’t anyone say ‘plague’?” Mr. Kramer said.

In 1983, he left Gay Men’s Health Crisis after much feuding with his fellow co-founders. In 1987, he was the driving force behind the founding of Act Up, which took a more hard-edge stance and relied on theatrics to get its points across.

Mr. Kramer and his fellow activists chained themselves to the balcony of the New York Stock Exchange and screamed about the high cost of AZT, the experimental AIDS drug.

They scattered the ashes of fallen comrades on the White House lawn and disrupted a Mass being given at St. Patrick’s Cathedral by Cardinal John O’Connor — a man who by night tended to AIDS victims and by day opposed condom distribution — wearing religious garb covered in blood.

“We lost count of how many times he resigned from Act Up over truly petty stuff,” said Peter Staley, a protégé who helped organize the memorial and spoke alongside two other Act Up veterans, Ann Northrop and Eric Sawyer.

“Yet all of this was family feuding,” Mr. Staley said. “We loved him.”

The writer Calvin Trillin, who attended Yale with Mr. Kramer and remained close to him, recalled how Mr. Kramer failed to show up to Christmas dinner at the Trillin family’s house one year, saying that he had been too disappointed in his straight friends’ response to AIDS to celebrate anything with them. Mr. Trillin recalled the reaction of his wife, Alice: “‘An odd sort of RSVP.’”

Tony Kushner, the playwright and screenwriter, gave a poignant speech that started with a joke: “I have a thing for cranky old Jews. He reminded me of my aunt Martha.”

He went on to describe how he also got scorched publicly by Mr. Kramer. His reaction to it differed from Dr. Fauci’s.

The war of the gay theater gods took place after Mr. Kushner’s epic play “Angels in America” won many awards, was made into a movie for HBO and brought him to the attention of Steven Spielberg, who hired Mr. Kushner to write several screenplays, including “Lincoln.”

Mr. Kramer believed firmly that President Lincoln was gay, but his sexuality did not figure much in Mr. Kushner’s and Mr. Spielberg’s portrayal. Over lunch at Union Square Cafe, Mr. Kushner said, Mr. Kramer pressed his argument, and his disapproval transformed into wrath.

Then came a blistering public attack. In interviews, Mr. Kramer called Mr. Kushner a sellout, a “gay artist” who had abandoned his responsibilities to gay people.

“I’m sort of surprised to find myself speaking at Larry’s memorial, because he blew up our truly lovely friendship,” Mr. Kushner said. “I begged him not to do it, but he couldn’t and he broke my heart.”

“We eventually reconciled,” Mr. Kushner continued, “and I told him I loved him, but I guess I’m ashamed to say that that was only partly true. I loved him, but I also didn’t. Not in the way I had before. I couldn’t find my old love for him again.”

“I wasn’t sure if I should say that today,” he added, “but all of us over the years have been to memorial services at which Larry spoke, and, well, I think I’m still on good behavior, comparatively.”

Sheila Nevins, the producer of an HBO documentary about Mr. Kramer, spoke of how she had largely been spared Mr. Kramer’s wrath. She got laughs when she described his rather lukewarm response to her memoir, “You Don’t Look Your Age, and Other Fairy Tales.” Mr. Kramer told her that “some of the stories” in the book were “good.”

She also spoke of watching him defy the odds again and again. In her estimation, he seemed to be saying, “I will not die.”

His final years were not easy. After going on protease inhibitors in the 1990s, Mr. Kramer’s T cells rebounded, but other health complications related to H.I.V. continued. In 2002 he got a liver transplant, but the side effects were brutal.

Many of the interviews for the HBO documentary took place in 2013. They show Mr. Kramer in a hospital bed, seemingly near death.

When he married his partner, David Webster, in 2013, the ceremony took place in the hospital room. Mr. Kramer couldn’t even say, “I do,” although he managed to give Mr. Webster a kiss when they were declared husband and husband.

The following year, HBO completed a filmed adaptation of Mr. Kramer’s 1985 play, “The Normal Heart,” directed by Ryan Murphy and starring Mark Ruffalo, Julia Roberts and Matt Bomer. Mr. Kramer was in such bad shape at the premiere that a number of people involved said privately that they believed he had willed himself to stay alive for its debut, expecting he would be dead within weeks.

Instead, he made it another six years.

Toward the end of the memorial, Mr. Webster took his turn at the lectern. He thanked Mr. Kramer’s various doctors in the audience for all the work they had done. And he told a version of their love story.

It left out the part about how they first dated in the 1970s and had an ill-fated romance that inspired a searing portrayal of him in Mr. Kramer’s 1978 novel, “Faggots.”

It included the part about how Mr. Kramer hired Mr. Webster in 1993 to find and design a house for him in Warren, Conn. His demand was for something on the water. Few were available.

“I suggested in real estate terms that he back off, maybe wait,” Mr. Webster said. “And, of course, he barked out at me, ‘You don’t understand. I’m a dying man. I want this now.’ The project did bring us together, and the dying man got his house to live.”

In 2020, he said, Mr. Kramer’s health began to fail again. By then, it was impossible for either of them not to be thankful for what they had shared, “including the ability to marry the one we love and, just like in every fairy tale, live happily ever after.”

Not that Mr. Kramer ever went soft.

“I know he’s still pointing fingers,” Mr. Webster said.