In White House councils, John Brennan has been privy to the most secret U.S. intelligence programs. Outwardly, he has been the administration's most public defender of one of President Barack Obama's most controversial practices -- the expanded use of armed drone aircraft to kill terrorism suspects overseas.
This is the second time that Obama has sought to put Brennan at the helm of the CIA, and his confirmation process is likely to revisit old controversies over U.S. counterterrorism measures undertaken by the administrations of Obama and George W. Bush.
Brennan, a 25-year CIA veteran, withdrew his name from consideration as Obama's first director of the agency in November 2008 following liberals' criticism that he had done too little to condemn the use by the Bush administration of interrogation techniques such as waterboarding, widely considered torture.
This time around, Brennan's defense of targeted killing by drones is likely to provide additional fodder for critics, although barring new revelations, he appears likely to be confirmed.
Deprived of the CIA post four years ago, Brennan, 57, became instead one of Obama's closest advisors on counterterrorism and homeland security. That proximity has made him a more powerful figure in the administration than the director of national intelligence - who will become his boss if he is confirmed.
Brennan, who grew up in New Jersey, is described by those who know him as a "straight arrow" and man of high morals.
"The word for John is 'intense'," said A.B. "Buzzy" Krongard, a former top CIA official who was once Brennan's boss there. "John's all about commitment."
His long working hours at the CIA and the White House are legendary. Obama, in announcing Brennan's nomination on Monday, quipped: "I'm not sure he's slept in four years."
Brennan pledged, if confirmed, to "make it my mission to ensure that the CIA has the tools it needs to keep our nation safe and that its work always reflects the liberties, the freedoms, and the values that we hold so dear."
PICTURE OF CLOSENESS
Brennan was at the president's side during some of the most significant security incidents during his first term.
The White House last week released a photograph of him briefing Obama on the elementary school massacre in Newtown, Connecticut. He is also visible in an iconic photo of top officials at the White House monitoring, in real time, the U.S. commando raid that killed al Qaeda leader Osama bin Laden in Pakistan in 2011.
Brennan is praised by former CIA officials who have worked with him. "John is a great choice - highly experienced, extremely dedicated, a person of integrity," said John McLaughlin, former acting CIA director.
But, by choosing him, Obama has given both liberals and conservative Republicans an opportunity to re-open the debate over Bush administration interrogation policies.
In a 2007 CBS television interview, while Brennan was out of government, he appeared to assert that enhanced interrogation techniques had produced useful information. "There have been a lot of information that has come out from these interrogation procedures that the agency has in fact used against the real hardcore terrorists. It has saved lives," he said.
Inside the CIA, where career intelligence officers consider it a point of pride to be above politics, employees will want to see whether Brennan's time at the White House has made him a more political figure.
"He will have to overcome the impression that he has become a political player who overachieved in spinning things to favor the president at the expense of the agency," a former CIA official said on condition of anonymity.
Shortly after the Navy SEAL raid that killed bin Laden, Brennan briefed the press, telling them that the al Qaeda leader had been killed in a firefight and had tried to use one of his wives to shield himself from the attackers.
"Here is bin Laden, who has been calling for these attacks, living in this million-dollar-plus compound, living in an area that is far removed from the front, hiding behind women who were put in front of him as a shield," he said at the time. "I think it really just speaks to just how false his narrative has been over the years."
The White House later retracted this account but said Brennan was speaking on the basis of the best information available at the time.
Although he rose through the ranks of the CIA's analytical wing, Brennan also worked on the agency's operational, spying side, and at one point served as the agency's chief of station in Riyadh, Saudi Arabia.
Said to be conversant in Arabic, Brennan played a hands-on role in Obama's Yemen policy, which was aimed at easing President Ali Abdullah Saleh from office while ensuring counterterrorism cooperation stayed on track. He traveled to Sanaa several times.
Senator Dianne Feinstein, who chairs the Senate intelligence committee that will hold a hearing on the nomination, said Brennan would make a "strong and positive director" of the CIA. In a statement, the California Democrat said that she would discuss with Brennan CIA detention and interrogation operations.
DEFENDER OF DRONES
In April 2012, Brennan publicly defended the U.S. campaign of lethal drone strikes as legal under international law. It was a rare public justification for classified operations that government officials infrequently discuss in public and that the CIA does not officially acknowledge.
In June 2011, Brennan alluded to drone strikes more opaquely, saying that over the prior year "not a single collateral death" had resulted from counterterrorism operations that were "exceptionally precise and surgical." Rights groups challenged the assertion that no civilians died during that period as a result of drone strikes.
The earlier comment came three months before a CIA drone killed Muslim cleric Anwar al-Awlaki, an American born member of al Qaeda, in Yemen. Another drone strike killed his 16-year-old U.S.-born son.
U.S. drone strikes in Pakistan have been a source of tension with the United States. One national security official familiar with Brennan's White House record said he is expected to favor aggressively moving forward with drone operations, even at the expense of offending Pakistani sensibilities.
The CIA and the U.S. military in recent years have been working more closely together, as in the bin Laden operation, which was run by the CIA but executed by the SEALs.
"Everybody looks at the CIA as insular, as sometimes difficult to establish relationships with, and so the degree to which the director can be one of the key forces for reaching out and breaking down those walls is really helpful," retired General Stanley McChrystal said in an interview with Reuters. "I think he can certainly be one of those types of leaders."