Shortly before 9 a.m. on March 11, 2014, Dianne Feinstein, the 80-year-old chair of the Senate Intelligence Committee, walked into the Senate chamber with a thick stack of papers and a glass of water. The Senate had just finished a rare all-night session a few minutes earlier, and only a handful of staffers were left in the room. Feinstein had given thousands of speeches over her career, but none quite like this.

“Let me say up front that I come to the Senate floor reluctantly,” she said, as she poked at the corners of her notes. The last two months had been an exhausting mix of meetings and legal wrangling, all in an attempt to avoid this exact moment. But none of it had worked. And now Feinstein was ready to go public and tell the country what she knew: The CIA had broken the law and violated the Constitution. It had spied on the Senate.

“This is a defining moment for the oversight of our intelligence community," Feinstein said nearly 40 minutes later, as she drew to a close. This will show whether the Senate “can be effective in monitoring and investigating our nation’s intelligence activities, or whether our work can be thwarted by those we oversee."

Two hours later and a few miles away at a Council on Foreign Relations event near downtown Washington, the CIA responded. “As far as the allegations of, you know, CIA hacking into Senate computers,” CIA Director John Brennan told Andrea Mitchell of NBC News, shaking his head and rolling his eyes to demonstrate the ridiculousness of the charges, “nothing could be further from the truth. I mean, we wouldn’t do that.”

Brennan was 58, but that morning he looked much older. He’d hobbled into the room on a cane following yet another hip fracture, and after some brief remarks he eased himself into a chair with obvious discomfort. Two years earlier in a commencement address at Fordham University, his alma mater, Brennan had rattled off a litany of injuries and ailments: In addition to his hip problems, he’d also had major knee, back, and shoulder surgeries as well as “a bout of cancer.” Years of desk work had resulted in extra weight and the sort of bureaucrat’s body that caused his suits to slope down and out toward his belt. “I referred the matter myself to the CIA inspector general to make sure that he was able to look honestly and objectively at what the CIA did there,” Brennan said. “And, you know, when the facts come out on this, I think a lot of people who are claiming that there has been this tremendous sort of spying and monitoring and hacking will be proved wrong.”

Mitchell, who had already asked him two questions about the allegations, pressed again. “If it is proved that the CIA did do this, would you feel that you had to step down?”

Brennan chuckled and stuttered as he tried to form an answer. Two weeks earlier, he had told a dinner at the University of Oklahoma that “intelligence work had gotten in my blood.” The CIA wasn’t just what he did; it was his “identity.” He had worked too hard to become director to give up without a fight. “If I did something wrong,” Brennan eventually told Mitchell, “I will go to the president, and I will explain to him exactly what I did, and what the findings were. And he is the one who can ask me to stay or to go.”

But Obama was never going to ask for his resignation. Not then, and not months later when the CIA inspector general’s report came back, showing that the agency had done what Feinstein claimed. Brennan was Obama's man. His conscience on national security, and the CIA director he’d wanted from the very beginning. Not even a chorus of pleas from Democratic senators, members of Obama’s own party, made any difference. John Brennan would stay, the untouchable head of America’s most powerful intelligence agency.

Brennan has been many things: a CIA official, a CEO, and even, briefly, a television pundit. He was a top official at the CIA during the torture years of the Bush administration, and the architect of Obama’s shadowy, controversial drone program. But for all that, he remains largely unknown, the gray heart of United States national security policy. Of the dozens of former and current government officials I reached out to, men and women from both the Bush and the Obama administrations, few seemed to have a handle on him. Some saw him as strong and principled, a warrior-priest who could do no wrong. Others saw him as a yes-man who sucked up to power and got lucky.

Several former colleagues, particularly in the CIA, refused to talk about him. He is vindictive, one explained through an intermediary: “He’ll come after me.” Another initially agreed to chat and then emailed me back a few days later, writing, “Unfortunately, I learned today that, because of my active security clearances and continuing work with the intelligence community, it would be best for me to decline your offer of an interview.”

Brennan himself was of little help. Through a spokesperson, he declined multiple interview requests over a series of months. Two years earlier, I’d argued that he was the wrong man for the CIA based on his counterterrorism approach in Yemen. But now I wanted to get a fuller sense of him, both as a person and as a director, and look at his entire career rather than just a single country. Brennan wasn’t interested. Even relatives were off-limits. At one point I sent his older sister a three-line email, explaining who I was and asking if she “might have some time to answer some questions about him and what he was like as a kid.” She never wrote back. But the next day I received an email from the CIA’s head of public affairs warning me against “harassing the director’s family.”

And yet in almost every public speech he’s given over the past 10 years, Brennan opens with a smattering of personal anecdotes, little crumbs of biographical detail that, along with everything else, form an almost kaleidoscopic portrait of the man and the country he serves. It all depends on the angle, the subtle shift in emphasis that changes everything: inside government or outside, friend or foe, enhanced interrogation techniques or torture, signature strikes or crowd killing, patriot or criminal.

This is Brennan’s story, his life and his career. But it's also ours. The excesses and mistakes of more than a decade of war, what we tolerate and what we don’t. What we’re willing to forgive and what we won’t. Politicians who don’t deliver on their promises, and well-intentioned individuals who bring about great harm. It’s about the man he is, and the country we’ve become. The institutionalization of a post-9/11 national security state, and the unending compromises of a country always at war.