Mary Caswell Orr (December 21, 1910 – September 22, 2006) was an American actress and author whose short story "The Wisdom of Eve", published in the May 1946 issue of Cosmopolitan, was the basis of the Academy Award-winning film All About Eve (1950). In private life, Orr used her married name, Mary Orr Denham.
Orr was born in Brooklyn, New York. She and her family relocated to Canton, Ohio when she was a girl. She studied at Syracuse University and the American Academy of Dramatic Arts in Manhattan.
"The Wisdom of Eve" was loosely based upon a woman who had been the secretary of Viennese actress Elisabeth Bergner. Orr wrote a radio adaptation which aired on NBC in 1949 which led to the movie being made. While she did not receive screen credit for All About Eve (she had sold the story to Twentieth Century Fox for $5,000), she did receive a Screen Writers Guild award for her original story. An alternative hypothesis for the Martina Lawrence-Elizabeth Bergner origin was the rivalry between Tallulah Bankhead and Lizabeth Scott (her understudy) during the production of Thorton Wilder's The Skin of Our Teeth. Broadway legend had it that Bankhead was being victimized by Scott, who was supposedly the real-life Eve Harrington.
In 1964, Orr and her husband, director-playwright Reginald Denham, adapted the short story into a play of the same name, which was produced off-Broadway in 1979. In 1970, a hit Broadway musical, Applause, was based on All About Eve and gave a credit to Mary Orr for the original story. She wrote a sequel to "The Wisdom of Eve" titled "More About Eve", which was published in Cosmopolitan in July 1951.