Petraeus has worked to pass on the lesson to a new generation. Marine Corps Lt. Seth Moulton helped Petraeus train the Iraqi Army, serving as the general's eyes and ears, poking into problems around Iraq. "In Iraq, . . . it is easy to blame people quickly," Moulton says. "But Iraq is complex, and there are 100 different motivations. General Petraeus has taught me even when there is an urgent problem to be calm, step back, and not react rashly."

From May 2004 until last September, Petraeus handled Iraq's toughest mission, re-creating its Army and police forces. At the security command, he inherited a mess. The Coalition Provisional Authority had dismissed the old army, forcing a new one to be built from scratch. Few of the existing Iraqi battalions were properly equipped. The battalions that had been deployed melted away in the face of the insurgency.

The jury is out on how successful Petraeus's efforts have been. But today, more than 197,000 Iraqi soldiers have been sent through basic training and equipped with rifles, body armor, and, in many cases, vehicles. With help from American units, Iraqi forces are beginning to execute their own missions.

The American military tests its leaders in a variety of jobs, promoting a few of the best from one rank to the next. But that was a luxury denied Petraeus as he helped find Iraqis to lead their nation's new Army. And the decision of who should lead battalions or companies has proved to be the most important. "We are approaching the point where . . . the key ingredient, increasingly, has become Iraqi leadership rather than another heavy machine gun," says Petraeus. "It is going to be Iraqi leaders who take it forward."

Yet perhaps there is no more difficult test of leadership in the military than when a soldier is killed. I asked Petraeus about the day at the memorial service. He acknowledged that at such events, his soldiers can read the sadness on his face. "It's just a fact that leaders are human beings," he says. "And the loss of a soldier is just the toughest blow for anybody with a leadership responsibility."

But Petraeus also knows the value of the stone face. On one night, in November 2003, 17 soldiers of the 101st were killed after two Black Hawk helicopters collided. Those 17 deaths weighed heavily on the general, and it showed. The stone face gave way. The day after the accident, at the 101st's headquarters, a young officer stopped his boss. "I know you are hurting," the officer told Petraeus. "However, their loss gives us that many more reasons to get it right."

For Petraeus, it was another lesson in leadership--this one learned from someone much younger. "You have to react," he says. "You honor the dead, you memorialize them, help the unit reach closure, then you redouble your efforts so that, obviously, their death was not in vain."

BORN: Nov. 7, 1952 EDUCATION: B.S., U.S. Military Academy at West Point; Ph.D., Princeton University FAMILY: Married, two children NEAR MISS: Petraeus was shot in training in 1991; the bullet just missed his heart. MOTTO: "Physical and mental toughness are...essential [to] leadership. It's hard to lead from the front if you are in the rear of the formation."