By Rebecca Shabad - 03/27/14 01:26 PM EDT
James Schlesinger, who served in several presidential Cabinets, has died at the age of 85, according to the Center for Strategic and International Studies (CSIS).
He served as a counselor and trustee at the Washington-based think tank.
He died at a Baltimore hospital on Thursday from complications due to pneumonia, according to The Washington Post. He lived in Arlington, Va.
Schlesinger served as CIA director under President Richard Nixon, Defense secretary under Nixon and President Gerald Ford and Energy secretary under President Jimmy Carter.
He was best known for leading the Pentagon from 1973–1975, when he focused on developing the United States’ nuclear strategy and the policy of “flexible response" to promote mutual deterrence. Schlesinger also worked on strengthening NATO’s capabilities in the midst of the Cold War.
Under Nixon, he also served as chairman of the Atomic Energy Commission. From 1977–1979, Schlesinger served as the nation’s first energy secretary under Carter.
Over the last 10 years, he was a member of the Homeland Security Advisory Council, the Defense Policy Board and a consultant to the Defense Department.
Schlesinger began his career in public serve in 1969, when he worked as assistant director of the U.S. Bureau of the Budget, which is known today as the Office of Management and Budget.