March 13, 2014 6:09 AM EDT

As a young Army officer in World War II, Roger Hilsman led commando missions deep behind enemy lines in Burma. After the war, he earned a doctorate in international relations at Yale. Armed with a warrior’s clout and an academic’s intellect, Hilsman joined the New Frontiersmen, bright young men who formed President John F. Kennedy’s foreign policy inner circle. In August 1963, as Assistant Secretary of State for Far Eastern Affairs, Hilsman helped draft a fateful cable to Henry Cabot Lodge Jr., U.S. ambassador to South Vietnam. Alarmed by raids on Buddhist pagodas by forces of South Vietnam’s Catholic President Ngo Dinh Diem, Kennedy’s advisers declared that Lodge must tell Diem to rid himself of his brother Nhu, who had orchestrated the raids. If Diem refused, they wrote, “we must face the possibility that Diem himself cannot be preserved.” Two months later, South Vietnam’s army deposed Diem. When it became public years later, the “Hilsman cable” was seen by many as an implied go-ahead for the coup, which opened the period of instability that may have brought on the escalation of the war in Vietnam. After Kennedy’s assassination, Hilsman, who died Feb. 23 at 94, taught at Columbia University for nearly 30 years.

–NATE RAWLINGS

This appears in the March 24, 2014 issue of TIME.

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