David Petraeus was a star on the battlefield, commanding the Iraq and Afghanistan wars, but was undone by "poor judgment" in engaging in an extramarital affair that led to his downfall as CIA director.

Just two days after his 60th birthday, Petraeus stepped down from the spy agency where he had held the top office since September 6, 2011.

"After being married for over 37 years, I showed extremely poor judgment by engaging in an extramarital affair. Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours. This afternoon, the President graciously accepted my resignation," Petraeus told the shadow warriors he commanded at CIA.

It was a stunning downfall for a revered military man who was seen as one of the top American leaders of his generation and was once considered a potential contender for the White House.

Petraeus was credited with pulling Iraq from the brink of all-out civil war and for battlefield successes in Afghanistan after overseeing a surge of 30,000 troops ordered by President Barack Obama in late 2009. He became known for counter-insurgency strategies that were seen as gaining ground against the Taliban in Afghanistan.

"I don't think he was professionally overrated. His were genuine accomplishments," said James Carafano, a war historian with the conservative Heritage Foundation think tank.

At the time of his nomination to the CIA post, some Washington insiders had said the White House wanted to find a high-profile position for Petraeus to ensure he would not be recruited by Republicans as a challenger to the 2012 Obama-Biden ticket.

When he was nominated to lead the CIA there were some concerns in intelligence circles that the high-profile four-star Army general might not be able to lead from the shadows as appropriate for a spy chief.

But once he took over the head office at the US spy agency, Petraeus kept a decidedly low public profile.

Senate Intelligence Committee Chairman Dianne Feinstein, a Democrat, expressed regret about the resignation of "one of America's best and brightest" and said it was an "enormous loss" for the country.

"At CIA, Director Petraeus gave the agency leadership, stature, prestige and credibility both at home and abroad. On a personal level, I found his command of intelligence issues second to none," she said.

After accepting his resignation about a year-and-a-half after nominating Petraeus to the CIA post, Obama said: "By any measure, he was one of the outstanding General officers of his generation, helping our military adapt to new challenges, and leading our men and women in uniform through a remarkable period of service in Iraq and Afghanistan, where he helped our nation put those wars on a path to a responsible end."

In 2010 Petraeus stepped into the breach as the new commander of US forces in Afghanistan to replace General Stanley McChrystal who was fired by Obama in a scandal over an article in which McChrystal and his aides made mocking comments about the president and some of his top advisers.

In 2009 Petraeus was diagnosed with early-stage prostate cancer and underwent radiation treatment. The media-friendly general joked at that time at a Washington event that reporters were only gathered "to see if the guy is still alive."

Petraeus, born in Cornwall, New York, lives in Virginia with his wife Holly. They have two grown children, a son who was an Army Ranger who served in Afghanistan, and a daughter.

Petraeus's wife, Holly, is an activist and volunteer who champions military families, and she continued that work after her husband retired from the military and moved to the CIA.

She currently is assistant director of the office of service member affairs at the Consumer Financial Protection Bureau, where she tries to keep unscrupulous lenders from taking advantage of military personnel. The bureau was championed by Harvard law professor Elizabeth Warren, who was elected to the Senate from Massachusetts this week.

Holly Petraeus is the daughter of four-star General William Knowlton, who was superintendent of the US Military Academy at West Point when Petraeus was a cadet.

She briefed the press at the Pentagon on her efforts recently and was introduced by Defense Secretary Leon Panetta, who called her "a true friend of the Department of Defense and a dedicated member of our military family."

Petraeus has four Defense Distinguished Service Medal awards, three Distinguished Service Medal awards, the Bronze Star Medal for valor, and the State Department Distinguished Service Award.

He has a doctorate in international relations from Princeton University.-Reuters