Born in Norfolk, Virginia to wealthy stockbroker Cornelius Hancock and heiress Garland Council Sullavan, Margaret Brooke overcame a muscle weakness in her childhood to go on to become a rebellious teenager at posh private schools. She went on to perform with the University Players at Harvard and made her Broadway debut in A Modern Virgin in 1931. Her Christmas Day marriage in 1931 to Henry Fonda lasted only a few months, and her later marriages to director William Wyler and agent Leland Hayward were also tempestuous. Two of her three children, Bridget and Bill, would spend some time in mental institutions, and friends noted that the collapse of her family life led to her breakdown. Her condition worsened over time, until she was discovered unconscious from barbiturate poisoning in a hotel room. Her death was ruled accidental by the county coroner.
Divorced Henry Fonda after two months. Mother-in-law of Peter Duchin. Mother of actress Brooke Hayward. Mother-in-law of Dennis Hopper, grandmother of Marin Hopper. As a child, family friend Peter Fonda had a crush on Sullavan's daughter Bridget. In adulthood, after Bridget committed suicide, he named his own daughter (Bridget Fonda) after her.