Anna Eleanor Roosevelt ( EL-in-or ROH-zə-velt; October 11, 1884 – November 7, 1962) was an American political figure, diplomat, and activist. She was the longest-serving first lady of the United States, during her husband Franklin D. Roosevelt's four terms as president from 1933 to 1945. Through her travels, public engagement, and advocacy, she largely redefined the role. Widowed in 1945, she served as a United States Delegate to the United Nations General Assembly from 1945 to 1952, and took a leading role in designing the text and gaining international support for the Universal Declaration of Human Rights. In 1948, she was given a standing ovation by the assembly upon their adoption of the declaration. President Harry S. Truman later called her the "First Lady of the World" in tribute to her human rights achievements.

Roosevelt was a member of the prominent and wealthy American Roosevelt and Livingston families and a niece of President Theodore Roosevelt. She had an unhappy childhood, having suffered the deaths of both parents and one of her brothers at a young age. At 15, she attended Allenswood Boarding Academy in London and was deeply influenced by its founder and director Marie Souvestre. Returning to the U.S., she married her fifth cousin once removed, Franklin Delano Roosevelt, in 1905. Between 1906 and 1916 she gave birth to six children, one of whom died in infancy. The Roosevelts' marriage became complicated after Eleanor discovered her husband's affair with her social secretary, Lucy Mercer, in 1918. Due to mediation by her mother-in-law, Sara, the liaison was ended officially. After that, both partners started to keep independent agendas, and Eleanor joined the Women's Trade Union League and became active in the New York state Democratic Party. Roosevelt helped persuade her husband to stay in politics after he was stricken with a paralytic illness in 1921. Following Franklin's election as governor of New York in 1928, and throughout the remainder of Franklin's public career in government, Roosevelt regularly made public appearances on his behalf; and as first lady, while her husband served as president, she greatly influenced the present scope and future of the role.

Roosevelt was, in her time, one of the world's most widely admired and powerful women. Nevertheless, in her early years in the White House she was controversial for her outspokenness, particularly with respect to her promotion of civil rights for African Americans. She was the first presidential spouse to hold regular press conferences, write a daily newspaper column, write a monthly magazine column, host a weekly radio show, and speak at a national party convention. On a few occasions, she publicly disagreed with her husband's policies. She launched an experimental community at Arthurdale, West Virginia, for the families of unemployed miners, later widely regarded as a failure. She advocated for expanded roles for women in the workplace, the civil rights of African Americans and Asian Americans, and the rights of World War II refugees.

Following her husband's death in 1945, Roosevelt pressed the United States to join and support the United Nations and became its first delegate to the committee on Human Rights. She served as the first chair of the UN Commission on Human Rights and oversaw the drafting of the Universal Declaration of Human Rights. Later, she chaired the John F. Kennedy administration's Presidential Commission on the Status of Women. By the time of her death, Roosevelt was regarded as "one of the most esteemed women in the world"; The New York Times called her "the object of almost universal respect" in her obituary. In 1999, Roosevelt was ranked ninth in the top ten of Gallup's List of Most Widely Admired People of the 20th Century, and was found to rank as the most admired woman in thirteen different years between 1948 and 1961 in Gallup's annual most admired woman poll. Periodic surveys conducted by the Siena College Research Institute have consistently seen historians assess Roosevelt as the greatest American first lady.