Von Kleist was born July 10, 1922, on his family estate Schmenzin in Pommerania in an area of northeastern Germany that is today Poland.
The von Kleist family was a long line of Prussian landowners, who had served the state for centuries in high-ranking military and administrative positions.
Von Kleist's father, Ewald von Kleist, was an early opponent of Hitler even before he came to power, and was arrested many times after the Nazi dictator took control in 1933. The elder von Kleist famously traveled to England in 1938, the year before World War II broke out, to try and determine whether other Western nations would support a coup attempt against Hitler, but failed to get the British government to change its policy of appeasement.
Despite his family's opposition to the Nazis, younger von Kleist joined the German army in 1940, and was wounded in 1943 in fighting on the Eastern Front.
During his convalescence, he was approached in January 1944 by Col. Claus von Stauffenberg, another officer from an aristocratic family, and presented with a plan to kill Hitler. Von Kleist had been chosen as the officer to model a new uniform for Hitler, and von Stauffenberg proposed that he wear a suicide vest underneath, and detonate it when he stood next to the dictator.
Years later von Kleist remembered explaining the suicide plot to his father, who paused only briefly before telling his 22-year-old son: "Yes, you have to do this."
"He got up from his chair," von Kleist remembered, according to an account by The New York Times, "went to the window, looked out of the window for a moment, and then he turned and said: 'Yes, you have to do that. A man who doesn't take such a chance will never be happy again in his life.'"
"Fathers love their sons and mine certainly did, and I had been quite sure he would say no," von Kleist recalled. "But, as always, I had underestimated him."
The suicide attack plan never came to fruition.
Months later, however, von Kleist was approached again by von Stauffenberg to take part in what would become known as the July 20 plot -- for the day in 1944 that the assassination was attempted -- which was brought to the big screen in 2008 in "Valkyrie," starring Tom Cruise as von Stauffenberg.
Von Kleist was supposed to play a key role as the person who was to carry a briefcase packed with explosives to a meeting with Hitler. In a change of plans, however, von Stauffenberg decided to plant the bomb himself.
Von Stauffenberg placed the bomb in a conference room where Hitler was meeting with his aides and military advisers at his East Prussian headquarters. Hitler escaped the full force of the blast when someone moved the briefcase next to a table leg, deflecting much of the explosive force.
Von Kleist remained in Berlin, charged with overseeing the arrest of officers and officials loyal to Hitler in the city.
But when news spread that Hitler had survived, the plot crumbled and von Stauffenberg, von Kleist's father, and scores of others were arrested and executed in an orgy of revenge killings. Some were hanged by the neck with piano wire. Von Stauffenberg was shot by firing squad.
Von Kleist himself was arrested, questioned at length by the Gestapo, and sent to a concentration camp, but then inexplicably let go and returned to combat duty.
Following the war, von Kleist founded the Ewald von Kleist publishing house, and became involved in public education on security issues and trans-Atlantic relations. In 1952 he founded the independent defense affairs association known as the Society for Military Studies, and the European Military Studies magazine in 1954.
In 1963 he founded what would become the annual Munich Security Conference -- a forum that still today brings together the world's top diplomats and defense officials, in an informal setting for talks on global security policy, and has long been considered the preeminent conference on NATO issues.
Von Kleist served as the conference's moderator until 1998, before handing it over to Chancellor Helmut Kohl's longtime foreign policy adviser Horst Teltschik, who has also since stepped down.
For his efforts leading the Munich Security Conference, von Kleist was awarded the U.S. Department of Defense's Medal for Distinguished Public Service in 1991, its highest award for a civilian.
His other decorations include Germany's Federal Order of Merit and France's Officier de la Legion d'Honneur.
His wife said funeral services would be private.
"My husband didn't want anything big," she said.
[ed.note: Additional reporting by TPM.]