Alger Hiss:
In 1948 Whittaker Chambers, a TIME magazine editor and former Communist Party member, testified to HUAC that several government officials were also former Communist or spies.
The most prominent official named by Chambers was Alger Hiss, a diplomat who had served in Roosevelt’s administration, attended the Yalta Conference, and taken part in organizing the United Nations.
After Hiss sued him for libel, Chambers testified before a grand jury that, in 1937 and 1938, Hiss gad given him secret document from the State Department.