He had operation to remove gallstones in 1953. The operation went wrong, and his health was ruined. He became Prime Minister in 1955 when Winston Churchill retired. He stopped being Prime Minister in 1957 when Harold Macmillan replaced him. The Suez Crisis of 1956 was a critical period. This and his health led up to his resignation as Prime Minister. Eden died of liver cancer, aged 79. His widow, Clarissa Eden, Countess of Avon, was born in 1920. She is a niece of Winston Churchill.