Llewellyn E. "Tommy" Thompson Jr. was a United States diplomat. He served in Sri Lanka, Austria, and, for a lengthy period, in the Soviet Union where his tenure saw some of the most significant events of the Cold War. He was a key advisor to President John F. Kennedy during the Cuban Missile Crisis. A 2019 assessment described him as " arguably the most influential figure who ever advised U.S. presidents about policy toward the Soviet Union during the Cold War."