Kennedy family confidant and former U.S. Defense Secretary Robert McNamara died in his sleep today at the age of 93.

"His age just caught up with him," his wife Diana, told Reuters. "He was not ill. He died peacefully in his sleep."

McNamara served as a key architect of the U.S. war in Vietnam — sometimes called "McNamara’s War" — which left 58,000 Americans dead. He served under presidents John F. Kennedy and Lyndon Johnson, and also advised JFK during the Cuban Missile Crisis in 1962, when the United States and the Soviet Union were on the brink of nuclear war. McNamara also became the first outsider to become president of the family-run Ford Motor company, served as president of the World Bank, and was a nuclear arms expert. As defense secretary, he boosted the Pentagon’s nuclear arsenal and streamlined the agency.

When Kennedy took office, only 500 Americans were in the South Asian nation, but by the time McNamara left his post in 1968, there were more than 500,000. Although he and other U.S. officials portrayed the Vietnam War as a necessary anti-communism battle in the Cold War, McNamara acknowledged later that they underestimated Vietnamese nationalism and opposition to the U.S.-backed government in Saigon.

"The conflict within South Vietnam itself had all of the characteristics of a civil war, and we didn’t look upon it as largely a civil war, and we weren’t measuring our progress as one would have in what was largely a civil war," he told CNN.

McNamara is survived by three children and his second wife, whom he married in 2004.