Kazan was a Commie who eventually became a liberal Democrat. He is remembered for testifying before a House Committee and naming persons who were Communists during the time that he was a member.
What is really funny is how this is called "McCarthyism" by the various slogan spewing naifs who write on the subject. Kazan testified during the Truman Administration in early 1952 while the Democrats controlled Congress. McCarthy did not become chairman of his committee until January 3, 1953.
Also Kazan testified before the House and not the Senate in which McCarthy was a member. Hilarious.