Michael Glenn Mullen (born October 4, 1946) is a retired United States Navy admiral, who served as the 17th chairman of the Joint Chiefs of Staff from October 1, 2007, to September 30, 2011. Mullen previously served as the Navy's 28th chief of Naval Operations from July 22, 2005, to September 29, 2007. He was only the third officer in the Navy's history to be appointed to four different four-star assignments; the other appointments being the Commander, U.S. Naval Forces Europe and Commander, Allied Joint Force Command Naples from October 2004 to May 2005, and as the 32nd vice chief of Naval Operations from August 2003 to August 2004. As Chairman, Mullen was the highest-ranking officer in the United States Armed Forces and diversified the top ranks of the Pentagon. He retired from the Navy after over 42 years of service. Since 2012, Mullen has been a visiting professor at Princeton University's School of Public and International Affairs.