Who is special counsel and former FBI Director Robert Mueller? originally appeared on abcnews.go.com

Former special counsel Robert Mueller has long been a source of curiosity for the general public as he and his team quietly investigated Russian interference in the 2016 presidential election.

Now, more than two years after his investigation began, the American public is hearing directly from him in a day of hearings on Capitol Hill.

The congressional hearings started with Mueller's opening remarks, where he referenced the findings made by his team and their resulting 448-page report. Mueller's report was delivered to Attorney General WIlliam Barr on March 22. Some details about the report’s contents were provided by Barr in a summary that was sent to Congress, but many questions were left unanswered.

PHOTO: Former Special Counsel Robert Mueller and former Deputy Special Counsel Aaron Zebley, right, go over notes as Mueller testifies before the House Judiciary Committee about his report, July 24, 2019 in Washington, D.C. (Chip Somodevilla/Getty Images) More

Here’s what you need to know about the man whose name has become synonymous with the probe.

A lifetime of public service

Mueller entered the national public spotlight as FBI director, a role he undertook on Sept. 4, 2001 — seven days before the Sept. 11 attacks.

Mueller, a registered Republican for most of his career, was nominated for the role under the Bush administration. He accepted the unusual request to extend his 10-year term during the Obama administration.

(MORE: LIVE UPDATES: Mueller contradicts Trump, says report did not exonerate him)

In both nomination hearings, he was confirmed with overwhelming Senate support. He served the second-longest term behind J. Edgar Hoover.

Years before joining the FBI as its director, Mueller served in the Marine Corps and led a rifle platoon in the Vietnam War. He received the Bronze Star, two Navy Commendation medals and a Purple Heart, according to his FBI biography.

(MORE: Attorney General William Barr defends handling of Mueller report, says release 'within a week')

Mueller holds a lengthy resume, complete with competitive academic accolades. Mueller went to Princeton University for his undergraduate degree, New York University for a master’s degree in International Relations and returned to school after concluding his military service for a law degree at the University of Virginia.

PHOTO: Special Counsel Robert Mueller leaves after attending church on March 24, 2019 in Washington, D.C. (Tasos Katopodis/Getty Images, FILE) More

After graduating in 1973, Mueller headed back into public service.

As a young lawyer, Mueller joined the U.S. Attorney's Office, first in California's Northern District and then in Boston. He served as chief of the criminal division in his San Francisco office and focused on major financial fraud in Boston, according to his FBI profile.

In 1990, Mueller joined the Department of Justice in Washington. He became the assistant to the U.S. Attorney General at the time, Dick Thornburgh, and oversaw major investigations into mob boss John Gotti and the bombing of Pan Am Flight 103, according to a Justice Department bio. Mueller also oversaw a shift in U.S. crime as computers and the internet began to take off, overseeing the creation of the department’s first cybercrime unit.

By early 2001, Mueller was tapped to serve as acting Deputy Attorney General, a position former FBI Director James Comey would also one day serve in as well. Soon afterward, Mueller was nominated to become director of the FBI — a position Comey would later hold as well.

PHOTO: A Sept.4, 2013 file photo showing incoming FBI Director James Comey, right, talking with retiring FBI Director Robert Mueller at the Justice Department in Washington,D.C. (Susan Walsh/AP Photo) More

(MORE: 7 key questions and answers about Mueller's report on Trump and Russia)

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