At different points in his career, Kellen analyzed postwar German soldiers, defectors from behind the Iron Curtain, Viet Cong who had been captured, and terrorists.
[1] He studied law in Munich before fleeing Germany with his family in March 1933 at age 19 to escape Nazi persecution.
[1] Kellen also worked for Radio Free Europe, interviewing defectors from behind the Iron Curtain to study life under the Soviet regime.
[1] In 1945, a stranger, who turned out to be painter Marc Chagall's daughter, approached Kellen in a Paris café and asked him to help save a stack of her father's canvases from the chaos of postwar Europe by bringing them to the United States, which he ultimately agreed to do.
[7] His opinion diverged markedly from the U.S. Administration's optimistic view, based in part on assessments by analyst Leon Gouré, that the war was winnable because of low enemy morale, Kellen joined RAND colleagues in writing an open letter to the U.S. government recommending the withdrawal of troops.
[7] Kellen wrote research papers and newspaper commentaries, as well as books including the biography Khrushchev (1961) and The Coming Age of Woman Power (1972), a study of male-female relationships.