Robert Todd Lincoln Secretary of War Signature on letter regarding purchase of flag for the Pennsylvania College at Gettysburg. Fine condition. Robert Todd Lincoln (August 1, 1843- July 26, 1926) was an American politician, lawyer, and businessman. He was the first son of President Abraham Lincoln and Mary Todd Lincoln. Born in Springfield, Illinois, United States, he was the only one of Lincoln 's four sons to live an adult life (his brother Tad Lincoln died shortly after his 18th birthday), and the only member of the family to survive into the 20th century. Lincoln attended Harvard University, and then served on the staff of Ulysses S. Grant as a captain in the Union Army.