• The 81-year-old has advised seven U.S. presidents, starting with Ronald Reagan.
• He's leaving public service to pursue the "next chapter" of his career.
• He first joined the NIH in 1968 at age 27 eventually taking over as director of the National Institute of Allergy and Infectious Diseases in 1984.
• Former President George W. Bush awarded Fauci the Presidential Medal of Freedom in 2008.

The nation's top infectious disease expert, Dr. Anthony Fauci, plans to step down from his roles running the National Institute of Allergy and Infectious Diseases and advising the White House as its chief medical advisor at the end of the year, he announced Monday.

Fauci has become a household fixture during the Covid-19 pandemic, battling back misinformation — sometimes from the highest levels of government. His steadfast commitment to science, challenging former President Donald Trump on everything from the use of hydroxychloroquine to mask mandates, made him a quasi-celebrity in the process.

The 81-year-old has advised seven U.S. presidents, starting with Ronald Reagan through the HIV/AIDS epidemic, West Nile virus, the 2001 anthrax attacks, pandemic influenza, various bird influenza threats, Ebola, Zika and, most recently, Covid and monkeypox.

Fauci, who also runs the NIAID Laboratory of Immunoregulation, said he has no intentions of retiring.

"After more than 50 years of government service, I plan to pursue the next phase of my career while I still have so much energy and passion for my field," Fauci said in a statement. "I want to use what I have learned as NIAID Director to continue to advance science and public health and to inspire and mentor the next generation of scientific leaders as they help prepare the world to face future infectious disease threats."

He first joined the National Institutes of Health in 1968 at age 27 where he quickly rose through the ranks and eventually took over as director of the National Institute of Allergy and Infectious Diseases in 1984. Former President George W. Bush awarded Fauci the Presidential Medal of Freedom in 2008.

Fauci called leading the NIAID through so many extraordinary health threats the "honor of a lifetime."

"I am very proud of our many accomplishments. I have worked with – and learned from – countless talented and dedicated people in my own laboratory, at NIAID, at NIH and beyond," he said. 'To them I express my abiding respect and gratitude."

Fauci was one of the very first people President Joe Biden said he called after he was elected was to office.

"During my time as Vice President, I worked closely with Dr. Anthony Fauci on the United States' response to Zika and Ebola," Biden said in a statement Monday. "I came to know him as a dedicated public servant, and a steady hand with wisdom and insight honed over decades at the forefront of some of our most dangerous and challenging public health crises."

During his tenure, Fauci never shied away from conflict. His Senate hearings were often peppered with terse exchanges with members of Congress, particularly with Sen. Rand Paul, R-Ky., who he once accused of inciting death threats against him and his family.

"What happens when he gets out and accuses me of things that are completely untrue is that all of a sudden that kindles the crazies out there and I have threats upon my life, harassment of my family and my children with obscene phone calls, because people are lying about me," Fauci told the Senate health committee at a January hearing.

At the height of the pandemic, Fauci was fielding more than 2,000 emails a day and working 24/7 on just three to four hours of sleep a night, he told friends and old colleagues in a trove of emails obtained through public records' requests by several media outlets.

Fauci was everywhere in American culture over the last 2½ years. Brad Pitt played him on "Saturday Night Live." The Atlantic called the then 79-year-old a "heartthrob" in an April 2020 article titled "America is Thirsty for Anthony Fauci."

His face adorned holiday ornaments, socks, donuts, T-shirts and fan art. Restaurants named drinks after him. The managers of Capo Italian Deli credit their Fauci Pouchy cocktail, vodka, elderflower and mint lemonade sold in an type of IV drip pouch, with helping to keep the restaurant afloat during the pandemic.

"Our society is really totally nuts," Fauci wrote in reaction to a piece documenting "Fauci Fever" and the online "sexualization" of the then-80-year-old virologist.

Fauci said in an email at the time that a March 2020 Washington Post article detailing his "cult following" was "truly surrealistic."

"Hopefully this all stops soon," Fauci wrote.

Disclosure: NBCUniversal is the parent company of CNBC and NBC, which broadcasts "Saturday Night Live."

Correction: Fauci has advised seven U.S. presidents. An earlier version misstated the number.