Kathleen Harriman Mortimer was an American journalist and socialite who played an important role in helping her father and President Franklin Delano Roosevelt with behind-the-scenes management of the American delegation to the Yalta Conference. Her father W. Averell Harriman was then the US Ambassador to the Soviet Union, and he played an important role in assisting Roosevelt, since the conference was held in Yalta, a Black Sea port part of the Soviet Union.