Prior to his appointment as Director of the Central Intelligence Agency, David Petraeus was a four-star general in the United States Army who capped a brilliant career by leading the campaigns that turned the tide of battle in both Iraq and Afghanistan. In his 37 years in the Army, Petraeus held leadership positions in airborne, mechanized, and air assault infantry units in Europe, the United States, and the Middle East. In 2003, he commanded the 101st Airborne Division in the assault on Baghdad. Hailed as "the world's leading expert in counter-insurgency warfare," he literally wrote the book on the subject. His Commander's Counterinsurgency Guidance is the standard work used today by military leaders facing armed insurgents. When President George W. Bush decided to change strategy in Iraq, he chose Petraeus to lead the surge. Petraeus's turnaround of an apparently hopeless situation made him the most admired leader in the United States military, one who has enjoyed enthusiastic support from political leaders of both parties. In 2008, he assumed leadership of United States Central Command, taking responsibility for all U.S. military operations in the Middle East, until President Barack Obama called on him to personally lead U.S. and NATO forces in Afghanistan. General Petraeus retired from the U.S. Army in 2011, and with the unanimous approval of the Senate, assumed duties as the 20th Director of the Central Intelligence Agency. He retired from the CIA in 2012 and is now a senior fellow at the Belfer Center for Science and International Affairs at Harvard University's John F. Kennedy School of Government.