David Petraeus resigned as the director of the Central Intelligence Agency today after admitting to carrying out an extramarital affair. Petraeus, a former Army general who became United States’ top spymaster last September, announced his resignation in a memo to CIA employees.

As an Army officer, Petraeus had led the U.S.’s wars in Iraq and Afghanistan, retiring last year as a four-star general widely praised as one of the best battlefield leaders of contemporary warfare.

“After being married for over 37 years, I showed extremely poor judgment by engaging in an extramarital affair,” Petraeus wrote. “Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours.”

In a statement, President Obama praised Petraeus’ tenure in both the Army and atop the CIA:

David Petraeus has provided extraordinary service to the United States for decades. 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. As Director of the Central Intelligence Agency, he has continued to serve with characteristic intellectual rigor, dedication, and patriotism. By any measure, through his lifetime of service David Petraeus has made our country safer and stronger.

Petraeus told Obama of his decision to step down yesterday afternoon, he wrote in his memo to CIA employees. Deputy CIA Director Michael Morell was named acting head of the agency.