Frances Folsom Cleveland

Frances Cleveland married Grover Cleveland and became first lady in her twenty-first year. She remains the youngest ever first lady, and is the only first lady to occupy that role twice, for both of her husband's non-consecutive terms as president.
After Grover's death, Frances Cleveland also became the first first lady to remarry. Her most notable activism later in life was working in favor of the United States entering World War I, organizing clothing drives for the poor during the Great Depression and, surprisingly, opposing women's suffrage.