Eleanor Roosevelt (1884-1962), wife of Franklin Roosevelt and niece of Teddy Roosevelt, was a political activist, diplomat, and the longest serving First Lady. She considered her biggest accomplishment to have been chairing the United Nations Human Rights Commission. This Commission created the 1948 Universal Declaration of Human Rights, which is still used today by the United Nations.
Other resources:
https://www.womenshistory.org/education-resources/biographies/eleanor-roosevelt
https://www.womenshistory.org/education-resources/biographies/eleanor-roosevelt
http://www.firstladies.org/biographies/firstladies.aspx?biography=33
https://www.fdrlibrary.org/er-biography
https://www.history.com/topics/first-ladies/eleanor-roosevelt