20th Century Fox

Henry Fonda and Jane Darwell in “The Grapes of Wrath,” a political manifesto based on John Steinbeck’s novel.

In “To Kill a Mockingbird,” Gregory Peck (with Mary Bad­ham) embodies the principle of legal equality.

United Artists

Gary Cooper and Grace Kelly in “High Noon,” a film that inspired the Polish Solidarity Movement.

Movie Star News via AP

Rod Steiger and Marlon Brando in “On the Waterfront,” a film that doesn’t hide its conservative politics.