It's been almost five months since Robert Mueller became the special counsel in the investigation into Russia's interference in the 2016 elections and whether President Donald Trump's campaign colluded with the Kremlin.
In Washington, Mueller has a reputation for being a tenacious investigator. Both Republicans and Democrats welcomed his appointment in May with bipartisan backing.
The increasing breadth of his investigation, however, has irked some Trump supporters.
Mueller's colleagues, meanwhile, say he has proven his bipartisan bona fides over the years. After all, he served under both Republican and Democratic presidents as FBI director and as an attorney in the Department of Justice.
As the probe into Trump and his associates heats up, here's a look at Mueller's history:
Born Robert Swan Mueller III in New York City in 1944, "Bob" grew up in the suburbs of Philadelphia, the elder brother to four younger sisters. Their father was an executive at DuPont. He captained the soccer, hockey, and lacrosse teams in high school.
Mueller pursued a career in medicine before he went off to fight in the Vietnam War. (Dennis Cook/AP)
Sources: FBI, St. Paul's School
Mueller went to undergrad at Princeton University, got his Master's in international relations from New York University, and graduated from the University of Virginia School of Law in 1973.
Mueller went to undergrad at Princeton University, got his Master's in international relations from New York University, and graduated from the University of Virginia School of Law in 1973. (University of Virginia School of Law/Facebook)
When one of his friends died in the Vietnam War, Mueller was inspired to join the military. He had been previously pursuing a career in the medical field.
Robert Mueller. (AP Photo/Andrew Harnik)
Source: Princeton Alumni Weekly
In 1968, Mueller enlisted in the Marine Corps and went on to become a decorated officer serving in Vietnam. He received a Bronze Star, a Purple Heart, the Vietnamese Cross of Gallantry, and two Navy Commendation Medals.
Mueller is a decorated war veteran. (Alex Wong/Getty)
After his military service, Mueller joined the San Francisco office of the international law firm, Pillsbury, Madison and Sutro. He worked as a litigator for three years.
Mueller received his law degree from the University of Virginia. (Evan Vucci/AP)
Then he spent more than a decade in government working for US Attorney offices in California, Massachusetts, and Washington, DC, gaining particular expertise in prosecuting white collar crime.
Mueller attends the swearing in of James Comey as the new FBI director in 2013. (Alex Wong/Getty)
Mueller is respected among his colleagues for his dedication to public service. In one example, a former associate was stunned when Mueller chose in 1995 to work in the homicide section of the US Attorney's Office in DC, which was perceived as a demotion for the highly credentialed lawyer.
Mueller points to a photo of Pan Am Flight 103 wreckage as the assistant attorney general in 1991. (Barry Thumma/AP)
Mueller reportedly explained his decision by saying, "There's just too many young people dying violently in this city, and I want to do my share to put an end to that."
Robert Mueller pauses after making an opening statement at the U.S. Senate Judiciary Committee hearing in 2013. (REUTERS/Larry Downing/File Photo)
Working on major cases involving financial fraud, terrorism, public corruption, money laundering, and narcotics conspiracies helped Mueller become a seasoned investigator over the years.
Mueller is now leading one of the most publicized investigations in the country as he looks into whether the Trump campaign colluded with Russia during the 2016 elections. (AP Photo/J. Scott Applewhite)
A week before 9/11, he was sworn in as the director of the FBI under President George W. Bush. The Senate confirmed him unanimously even though he was diagnosed with prostate cancer at the time.
Mueller served under Bush for the majority of his FBI career. (Robert Trippett/Getty)
Source: CNN and CBS News
In 2002, Mueller was the subject of lawsuits filed by Muslim immigrants who claimed they had been beaten and abused by officials in immigration detention centers because of policies the Bush Administration implemented after 9/11. The Supreme Court ruled in 2017 that Mueller, along with John Ashcroft, the former attorney general, could not be sued.
Mueller is praised across the political aisle. (Thomson Reuters)
Source: The New York Times
In 2004, there was a standoff between Mueller and Bush after he and other Justice Department officials threatened to resign if changes were not made to the National Security Agency's domestic wiretapping program. Bush conceded in the end.
Mueller stands with Bush in the Rose Garden. (Mark Wilson/Getty)
Source: Washington Post
After Mueller finished his 10-year term in 2011, President Barack Obama asked him to stay for two more years. He was the longest-serving FBI director since J. Edgar Hoover, who founded the bureau in 1935.
President Barack Obama, Attorney General Eric Holder, Homeland Security Secretary Janet Napolitano and FBI Director Robert Mueller attend the National Peace Officers' Memorial Service Washington. (Chip Somodevilla/Getty)
Mueller is often praised on Capitol Hill for his service under both Republicans and Democratic presidents.
Mueller confirmed that the FBI uses drones for domestic surveillance during a hearing on FBI oversight in 2013. (Alex Wong/Getty)
Even though Mueller is a Republican, many Democrats admire him. Earlier this year, Democratic Senator Jim Himes said, "There's not anybody with as much credibility internally or whose integrity is as unimpeachable as Bob Mueller."
Mueller's colleagues have praiseworthy things to say about him. (Mark Wilson/Getty)
Sources: The Washington Post, The Washington Post
But it's Mueller's breadth of experience with high-profile litigation that has earned him the most respect.
Mueller attends a funeral at Arlington Cemetery in 2011. (Brendan Smialowski/Getty)
During his private and public sector careers, Mueller presided over many noteworthy cases, including the prosecutions of Panama's former dictator, Manuel Noriega, and New York City crime boss, John Gotti.
Mueller has presided over many high-profile cases throughout his career. (Thomson Reuters)
In 2015, NFL Commissioner Roger Goodell put Mueller in charge of investigating the widely-publicized Ray Rice incident. Rice, then a running back for the Baltimore Ravens, was indicted on third-degree aggravated assault for beating his fiancée, although the charges were later dropped.
NFL Roger Goodell greets football fans. (Sean M. Haffey/Getty)
Source: Mueller NFL Report
In March, Attorney General Jeff Sessions recused himself from all Russia-related investigative matters after failing to disclose his campaign-trail meetings with Russian Ambassador Sergey Kislyak, setting off a chain of events.
Attorney General Jeff Sessions during a press conference. (Alex Wong/Getty Images)
Source: Business Insider
In May, Trump fired FBI Director James Comey, who testified before Congress that he thought it was because of the investigation he was conducting into Trump and his associates' ties to Russia. Sessions had recommended his firing, so his recusal was then thrown into question.
Comey testified before the Senate Intelligence Committee on June 9. (Drew Angerer/Getty Images)
Sources: Business Insider, Business Insider
On May 17, Deputy Attorney General Rod Rosenstein appointed Mueller special counsel to take over the Russia investigation, including "any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump."
James Comey and Robert Mueller walk together outside the White House. (Win McNamee/Getty)
Sources: Business Insider, DOJ
Some Trump allies have criticized Mueller's closeness to Comey and accused him of overreaching in the investigation. In response to calls for his firing, senators introduced bipartisan legislation that would allow Mueller to challenge the Department of Justice in court if he were removed.
A Republican and a Democrat co-sponsored the bill in the Senate. It hasn't passed yet. (Jeff Chiu/AP)
Sources: LA Times, New York Post, WBUR
Although updates on the probe have periodically leaked to the press, Mueller has remained tight-lipped. It's unclear how close he may be to concluding the case, but some estimates say it could take at least a year.
The Justice Department appointed Mueller as Special Counsel in May 2017. (Aaron Bernstein/Reuters)
Sources: USA Today, Reuters