Former Secretary of Defense Harold Brown, who served in the Carter administration, died Friday at age 91.

The Department of Defense and the Rand Cooperation, where Brown served on the board of trustees for more than 35 years, released statements on Saturday mourning his death and lauding his contributions to the country.

"He shaped our nation’s military for more than two decades, revolutionizing the development of naval munitions, renovating America’s post-Vietnam War weapons platforms, developing stealth aircraft, and leading nuclear weapons research," Acting Defense Secretary Patrick ShanahanPatrick Michael ShanahanTop US general to meet with Google over China security worries 737 crisis tests Boeing's clout in Washington The Hill's Morning Report - Trump's intraparty feuds divide Republicans MORE said in a statement.

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"As Secretary of Defense, Dr. Brown’s steady leadership piloted our nation through a consequential segment of the Cold War," he continued. "His focus on deterrence through a strong nuclear triad facilitated long-term peace and stability in the United States and Europe."

Brown served as a key player in navigating the Cold War and the Iranian hostage crisis. In addition to his four years as Defense secretary, he served as the head of the Air Force, director of defense research and engineering and president of the California Institute of Technology.

Brown had a background as a scientist, and worked as a nuclear physicist and weapons designer.

“Harold Brown understood, perhaps better than any defense secretary before him, the technological complexities and unprecedented dangers of modern warfare,” Michael D. Rich, president of the Rand Corporation, said in a statement.