The director of the National Institute of Allergy and Infectious Diseases said on Monday that he planned to leave government service in December to pursue the next chapter of his career.

It was not surprising that Dr. Fauci made the announcement. He has been saying for a while that he was going to retire. He said in an interview that he was not retiring in the traditional sense, but would devote himself to traveling, writing and encouraging young people to enter government service.

Dr. Fauci said in the interview that he wants to do some things outside of the federal government if he is healthy.

Mr. Biden said that Dr. Fauci was a dedicated public servant and a steady hand. When Mr. Biden was vice president, there was an outbreak of the mosquito-borne disease.

The president said that lives have been saved because of Dr. Fauci.

Few scientists have had an impact that long. When Lyndon Johnson was president, Dr. Fauci became the director of the infectious disease branch of the National Institute of Health.

Every president since Ronald Reagan has been advised by Dr. Fauci, who has been an expert on politics and science. He said that his proudest accomplishment was his work with Bush in developing a global program to combat H.I.V./AIDS. The Presidential Medal of Freedom was awarded to Mr. Bush by his father George Bush.

The politics of the Trump era made Dr. Fauci a target. It would have been difficult for the president to fire Dr. Fauci because he is not a political appointment. Conservatives viewed Dr. Fauci as a symbol of masks and lock downs.

ImagePresident George W. Bush honored Dr. Fauci with a Presidential Medal of Freedom in 2008.
President George W. Bush honored Dr. Fauci with a Presidential Medal of Freedom in 2008.Credit...Ron Edmonds/Associated Press
President George W. Bush honored Dr. Fauci with a Presidential Medal of Freedom in 2008.

Senator Paul accused Dr. Fauci of lying about his institute's funding of research in China that led to the emergence of the coronaviruses. If anyone is lying, it is you, Dr. Fauci said. If the Republicans win control of Congress, they will investigate Dr. Fauci.

Dr. Fauci said that he had no intention of working in the pharmaceutical industry, as some of his critics have said. After Mr. Biden asked him to serve as his medical adviser, he considered stepping down.

"So I stayed on for a year, thinking that at the end of the year, it would be the end of Covid, and as it turned out, that's not exactly what happened" I realized that there are things I want to do after two years here.

Dr Fauci leads an immunology laboratory and also runs the allergy and infectious diseases institute. He said the president was very gracious about it and that he had told Mr. Biden.

Dr. Fauci did not say when he would leave. He hoped that by staying through the fall and early winter, the US would be able to live with the coronaviruses in a steady state.

400 deaths per day is not good for him. We have to do better than that. I don't think I can say that I'm happy with where we are. I hope that things will get better over the next few months.

He didn't have a publisher yet while he was working on his memoir. He said in an interview that he was not allowed to work with a publisher while he was still employed by the government.

Dr Fauci has been a government scientist for more than 50 years. He was best known for his work on H.I.V./ AIDS. Activists accused him of being responsible for the deaths of gay men because he didn't move quickly enough to get new treatments approved.

He befriended a lot of those people. Peter Staley, one of the activists, said in an email message that he had put an effigy of his head on a stick in front of his building. Mr. Staley said that he had never met a more decent person.

Dr. Fauci cared for AIDS patients when most of them died. He recalled arriving at the bedside of an AIDS patient who had lost his vision, in a documentary released by National Geographic.

His voice broke as he told the story. The filmmakers wanted to know why it was bothering him now. He gathered himself. He paused to think about post-traumatic stress syndrome. It is what it is.

Dr. Fauci was a household name in the early days of the coronaviruses epidemic. A petition to name him People magazine's "Sexiest Man Alive" received more than 30,000 signatures.

In an interview this year, Dr. Fauci said that some of Mr. Trump's aides tried to pillory him by saying that everything he said was incorrect. He didn't say anything bad about Mr. Trump.

ImageDr. Fauci catapulted into the spotlight during briefings at the White House when the coronavirus pandemic took hold in the United States in 2020.
Dr. Fauci catapulted into the spotlight during briefings at the White House when the coronavirus pandemic took hold in the United States in 2020.Credit...Doug Mills/The New York Times
Dr. Fauci catapulted into the spotlight during briefings at the White House when the coronavirus pandemic took hold in the United States in 2020.

They tried to destroy me instead of throwing me out. He said that the person who is telling the truth based on science becomes the enemy if they are propagating lies.

Dr Fauci said in his statement that he would use his remaining months in government to put his full effort into his current responsibilities and to help prepare his institute for a leadership transition.

Some of the most talented scientists in the world are served by N.I.H., and I have no doubt that I am leaving this work in very capable hands.