Short answers, pulled from the story.
Elia Kazan was a Greek-American film and theatre director born in Constantinople on the 7th of September, 1909, and described by The New York Times as "one of the most honored and influential directors in Broadway and Hollywood history." He co-founded the Actors Studio in 1947, helped introduce Method Acting to Hollywood, and launched the careers of Marlon Brando, James Dean, and Warren Beatty, among many others.
In April 1952, Kazan testified before the House Un-American Activities Committee and named eight former Group Theatre members he said had been Communists, including Clifford Odets, Morris Carnovsky, and Paula Miller. He had himself been a Communist Party member during 1934-1936 and later took out an advertisement in The New York Times urging others to follow his example.
Seven of Kazan's films won a total of 20 Academy Awards, and his actors alone received 24 Oscar nominations and won nine. Kazan himself won Best Director twice, for Gentleman's Agreement in 1947 and On the Waterfront in 1954.
When Kazan received an Honorary Oscar at the 71st Academy Awards in 1999, the audience was sharply divided because of his 1952 HUAC testimony. Actors including Nick Nolte, Amy Madigan, and Ed Harris refused to applaud, while 250 demonstrators picketed outside. Others, including Warren Beatty, Meryl Streep, and Karl Malden, gave him a standing ovation.
Kazan directed Brando in A Streetcar Named Desire (1951), which received twelve Oscar nominations and won four; Viva Zapata! (1952); and On the Waterfront (1954), which received twelve Oscar nominations and won eight, including Best Actor for Brando. Brando later wrote that Kazan was "the best actors' director by far of any I've worked for."
Kazan saw James Dean perform on stage in New York, then cast him as the lead in East of Eden (1955) after an audition, also giving him an exclusive contract with Warner Bros. Dean flew back to Los Angeles with Kazan in 1954 carrying his clothes in a brown paper bag; it was the first time Dean had ever flown. East of Eden was the only completed film Dean ever saw before his death at age 24.