Petraeus's experience in Mosul helped cement his belief in adaptability. It was soon after the fall of Saddam Hussein's regime when the 101st got the order to go to Mosul. In essence, Petraeus was charged with restarting the city's economy, getting civic institutions on their feet, building a local security force, and creating a working democracy.

Under Petraeus, the officers of the 101st found themselves playing far out of position. One of his artillery officers was charged with figuring out how to get the region's oil flowing again. Some officers supervised cement factories, others electricity generation. Soldiers who had studied military aviation tactics found themselves figuring out how to administer a university. Petraeus himself supervised the city's first real elections.

College lessons. Petraeus says he drew on his academic training in both economics and political theory. One of the first tasks in Mosul was to start paying the salaries of government employees--basically everyone in the city. But Petraeus realized, in no small part from his Princeton days, that if no new goods flowed into the city, yet the amount of money dramatically increased, inflation would follow. The solution, Petraeus says, came from the Iraqis: reopen the border with Syria.

But nothing there was easy. Petraeus had to work hard to convince the locals that his ideas about democracy could help them. "The great thing about graduate school is nobody is in the least impressed by rank, they're impressed by the persuasiveness of one's ideas," Petraeus says. "And frankly, with the people of Mosul, you realized it's not enough to fall back on rank. What they want is logic and understanding."

Fit for duty. Petraeus puts a strong emphasis on physical fitness. Many of his soldiers dread the invitation to go on a run with him because it takes so much energy to keep up. Petraeus has survived two nearly fatal injuries during his career, and he credits being in top shape for his full recovery. But, Petraeus says, there is a wider lesson, too: "Leaders must master the essential skill of their organization."

Earlier in his career, Petraeus was criticized as being a "Washington officer," in part because he had served as an aide to some of the nation's top generals. His years in Iraq have quieted much of that criticism, and Petraeus says the time spent with top officers was critical to his own leadership. Petraeus was at the side of Gen. Hugh Shelton, the chairman of the Joint Chiefs of Staff, during the conflict in Kosovo. By nature, Petraeus bubbles over with ideas and Shelton remembers him as tireless. "David Petraeus," says Shelton, "is a high-energy individual who likes to lead from the front, in any field he is going into."

That remains true, but Petraeus says that Shelton also taught him to project calm. "When the situation was the toughest," Petraeus says of Shelton, "he sought to provide a calming influence and a degree of encouragement, energy, and quiet confidence." Petraeus claims his greatest weakness remains his impatience. Often a strength, it must sometimes be throttled back, he says, particularly when he meets with Iraqi officials, who have their own way of doing business.