Robert Todd Lincoln, (1843-1926) was the first child of Abraham Lincoln and Mary Ann Todd. Born on August 1, 1843 in Springfield, Illinois, United States, he was the only one of President Lincoln's four sons to reach adulthood.

Robert Lincoln graduated from Phillips Exeter Academy, then studied at Harvard University from 1861 to 1864 following which he enrolled in Harvard Law School. However, he did not graduate and in 1865 joined the Union Army. He held the rank of Captain, serving in the American Civil War as part of General Ulysses S. Grant's staff.

Following his father's assassination, in May of 1865 he, his brother Thomas (Tad) Lincoln (1853-1871), and their mother moved to Chicago where Robert completed his law studies at the University of Chicago. He was admitted to the bar on February 25, 1867. The following year he married Mary Eunice Harlan (1846-March 31, 1937), the daughter of Senator James Harlan and Ann Eliza Peck of Mount Pleasant, Iowa. They had two daughters and one son:

In 1877 he turned down President Rutherford B. Hayes' offer to appoint him Assistant Secretary of State but he did accept to become the United States government Secretary of War from 1881 to 1885, serving under Presidents James Garfield and Chester A. Arthur. In addition, he served as the ambassador to the United Kingdom from 1889 to 1893 under President Benjamin Harrison after which he returned to private business as the President and Chairman of the Board of the Pullman Palace Car Company where he worked until his retirement in 1922. He made his last public appearance at the dedication ceremony in Washington, D.C for his father's memorial on May 30th of that year.

Robert Todd Lincoln died at his Manchester, Vermont home on July 26, 1926 and was later interred in Arlington National Cemetery next to his wife Mary and their son Jack who died of blood poisoning at the age of 16 in London, England.