General David Petraeus has resigned as chief of the Central Intelligence Agency because of an extramarital affair.

General Petraeus wrote in a letter to CIA staffers that he submitted his resignation in person to President Barack Obama Thursday. Petraeus writes that he used extremely poor judgment and that such behavior is unacceptable in a leader.

The general says it has been the greatest of privileges to serve in the CIA and he thanked its workers for what he called their exceptional service.

President Obama says through Petraeus's lifetime of extraordinary service in the military and as American intelligence chief, the country was made safer and stronger.

The 60-year-old Petraeus joined the military right out of high school when he entered the U.S. Military Academy at West Point.

Petraeus rose to the rank of a four-star general, commanding the multi-national force in Iraq. He later became commander of U.S. forces in Afghanistan as well as one of the world's best known military leaders before taking over the CIA last year.