The man tapped by President Barack Obama to lead the Pentagon - knows the department well. Ashton Carter served for four years in senior Pentagon jobs and was the No. 2 official at the Pentagon from October 2011 to December 2013, when he stepped down.

Carter, a physicist br training, has held the job of the Pentagon's chief arms buyer. The graduate of Yale and Oxford, who was a Rhodes scholar, also served as assistant secretary of defense for international security policy under President Bill Clinton.

If confirmed by the Senate, Carter will be Obama's fourth defense secretary. He replaces Chuck Hagel who resigned under pressure after less than two years at the helm of the Defense Department.