Ashton Carter will be nominated as Deputy Secretary of Defense by President Obama, the White House announced Tuesday. William Lynn, the current Deputy Defense Chief, is retiring. This would make Carter Defense Secretary Leon Panetta's number two man.

So, what do we know about him?

Carter, 56, has served the United States in various positions in security, intelligence and defense. He is currently the Under Secretary of Defense for Acquisition, Technology and Logistics, a position he has held since 2009.

He served the two previous presidents. He worked in the Clinton administration as the Assistant Secretary of Defense for International Security Policy from 1993 to 1996. His duties included being responsible for the Nunn-Lugar program, which resulted in the removal of all nuclear weapons from Ukraine, Kazakhstan and Belarus. From 2006 to 2008, he served the Bush administration as a member of then-Secretary of State Condoleezza Rice's International Security Advisory Board.

Carter has also held positions in higher education, including the Massachusetts Institute of Technology, Rockefeller University and Harvard University's John F. Kennedy School of Government. He has written op-eds for The Wall Street Journal and The Boston Globe and authored several books on security and defense.

He received the Department of Defense's Distinguished Service Medal twice, the department's highest award, as well as the Defense Intelligence Medal.

Carter spoke about the need for improved efficiency in the Department of Defense in a speech hosted by the Center for a New American Security (CNAS) in February of this year. "We are in the habit of taking forever, and forever costs an awful lot," he said. 

Carter's interest in security matters certainly goes back a long way. He received his bachelor's degrees from Yale University, where he studied physics and medieval history. He was a Rhodes Scholar at Oxford University, from where he received his doctorate in theoretical physics.