The House Un-American Committee. Established in 1938 to investigate the eve of World War II.
Began a postwar probe of Communist infiltration of government agencies, and more specifically, a probe of the Hollywood movie industry.
Movies had tremendous power to influence the public. 1947 HUAC charged that numerous Hollywood figures had communist leading that affected their film making.
Some Hollywood personalities were or had been members of the Communist party. Others of the industry had openly supported various causes and movements with philosophical similarities to communism.
With government encouragement, Hollywood had produced some movies favorable to the Soviet Union and its people. This was during the war , when the United States and Soviets had been allies.