The general appeared to have developed a special bond with his enthusiastic but untested biographer, aides say, and Broadwell appeared willing to take full advantage of her special access.
"I found her relationship with him to be disconcerting," said a former aide to the Petraeus, one of several who insisted on anonymity in order to speak candidly about his former boss. "Those who worked for him never tried to leverage our relationship with him. It seemed to a lot of us that she didn't have that filter."
The full extent of the bond was exposed Friday when Petraeus, 60, abruptly resigned as CIA director, acknowledging in a statement that he had been unfaithful to his wife of 38 years. The resignation marked a stunning career reversal for Petraeus, a storied commander whose successes in Iraq and Afghanistan had made him a hero to millions of Americans and won him a perennial mention as a possible future candidate for U.S. president.
Telephone and e-mail requests for interviews with Broadwell were not returned.
For Broadwell, who is also married, the startling turn of events has reportedly been painful as well. After writing a best-selling and highly laudatory book about Petraeus, she appears to have initiated the series of events that led to his public humiliation. Investigators say threatening e-mails from Broadwell to another woman led to the discovery of the affair between the biographer and her subject. It is an outcome made more poignant because she has been - and remains - zealous in her devotion to the general, friends and colleagues say.
"She was relentlessly pro-Petraeus," said a longtime Afghan policy expert who met Broadwell in Kabul. "There was no room for a conversation of shortcomings of the Petraeus theology. She wasn't a reporter. She struck me as an acolyte."
According to her own account, Broadwell met Petraeus in 2006, when she was a graduate student at Harvard's Kennedy School of Government. Petraeus had gone to Harvard to talk about his experiences as commander of the 101st Airborne Division during the 2003 invasion of Iraq and about a new counterinsurgency manual he was developing. After the presentation, Broadwell - an Army reservist and, like Petraeus, a West Point graduate - was invited to attend a dinner with the general and a few other students.
"I introduced myself to then-Lt. Gen. Petraeus and told him about my research interests," she would write in her book, "All In: The Education of Gen. David Petraeus." She said the general handed her his business card and offered to put her in touch with other researchers working on similar issues. (Vernon Loeb, the local editor of The Washington Post, was a co-author of the book.)
"I later discovered that he was famous for this type of mentoring and networking, especially with aspiring soldiers-scholars," she wrote.
In 2008, while pursuing a doctorate, Broadwell decided to write a case study of Petraeus' leadership style. After several e-mail exchanges, Petraeus, an avid runner, invited her to discuss her project during a run along Potomac River in Washington. The two discovered a common bond: Broadwell, a high school track star who won awards for fitness at West Point, earned the general's admiration by keeping up with his grueling, six-minute-mile pace.
"I think I passed the test," she would later say, "but I didn't bother to transcribe the interview."
Soon after, Broadwell decided to turn her dissertation into a book. With the blessing of Petraeus, she made the first of about a half-dozen extended trips to Afghanistan to spend time with him and interview members of his senior staff and field commanders.
Her trips were not without controversy. Aides were stunned by the close access that Broadwell was granted - and that she occasionally flaunted. At the same time, some were unimpressed by her reporting style and thin journalistic résumé.
"Her credentials didn't add up," said a former Petraeus staff member who was interviewed a number of times by Broadwell. "I was underwhelmed. It was surprising to me that she was his official biographer."
Peter Mansoor, a former executive officer on Petraeus's staff, said he thought the general's uncharacteristic confidence in an untested writer was "strange."
"My gosh, if you are going to have someone interview everyone who has ever touched you in your life, chose someone who has written a biography or at least a history book," he said in an interview Saturday.
There were other controversies as well. Former aides say Broadwell's attire - usually tight shirts and pants - prompted complaints in Afghanistan, where Western-style attire can offend local sensibilities. Her form-fitting clothes made a lasting impression on longtime Afghan hands, and Petraeus once admonished her, through a staffer, to "dress down," a former aide recalled.
"She was seemingly immune to the notion of modesty in this part of the world," said a general who served in Afghanistan while Petraeus was commander there.
Officers close to Petraeus grew concerned about her posts on Facebook, which they believed sometimes divulged sensitive operational details. The posts, intended for friends back home, were often playfully written and aimed at showing off her adventures in the war zone.
Some senior officers thought Broadwell, who held a security clearance and had served as an Army intelligence officer, should have known better.
Despite the obvious closeness between the general and the biographer, former aides said, that the two could be having an affair seemed unthinkable, mainly because Petraeus came across as the consummate gentleman and family man.
"I spent a lot of time with him, and I never heard him say, 'Wow, she was hot,' " one former aide said. "I never recalling hearing him say anything crass or even mentioning the good looks of a person."
Broadwell impressed others who met her because of her hard work, intelligence and seemingly inexhaustible energy, traits that often are associated with Petraeus. Journalists who befriended her were struck by her idealism and passion for favorite causes, including a wounded-warrior project that she has promoted, sometimes with Petraeus' help.
"Paula is an impressive woman - high energy, smart, a classic overachiever," said Thomas E. Ricks, who came to know Broadwell while researching his new book, "The Generals," which is in part about Petraeus.
Other friends and acquaintances also described her as driven and high-achieving. Broadwell, a North Dakota native, was valedictorian and prom queen of her high school graduating class and a member of the state's all-star basketball team. She graduated from West Point with a degree in political geography and systems engineering and finished first in her class in fitness.
After college, she served for more than a decade in the Army, attaining the rank of major before leaving the military to attend Harvard. Through her 30s, while traveling for her book and raising two children, she managed to compete in Ironman triathlons.
On an official website for her book, which has since been taken down, Broadwell talks about her competitive streak. "I was driven when I was younger," she said. "Driven at West Point where it was much more competitive in that women were competing with men on many levels, and I was driven in the military and at Harvard, both competitive environments."
In promoting her book this year, Broadwell went on a nationwide media tour that included an appearance on "The Daily Show With Jon Stewart" in January. She challenged Stewart to a push-up contest, and he agreed, saying he would donate to a charity for wounded veterans if she beat him. Her husband, Scott Broadwell, a radiologist, was brought on stage, and she beat both of them.
Broadwell, who turned 40 on Friday, lives in Charlotte, N.C., with her husband and her two sons. As the news of Petraeus' resignation made national news Friday, Broadwell and her husband were visiting friends in Virginia, celebrating her birthday with dinner at the Inn at Little Washington, one of the region's most famous and most expensive restaurants.
In the acknowledgments at the conclusion of her book, Broadwell credited her successes in part to her husband, an "amazing and supportive partner," who "played Mr. Mom for our two boys while I was in Afghanistan." Then she thanked Petraeus for his cooperation, saying his "willingness to indulge my endless questions . . . provided me with a once-in-a-lifetime education."
"I am grateful for his candor, trust and support," she wrote.