A head-and-shoulders portrait of Abraham Lincoln, the 16th President of the United States and first President from the Republican Party, from 1863. Considered one of the greatest Presidents of the U.S., Lincoln is most famous for outlawing slavery in the Confederacy through the Emancipation Proclamation and the nation with the Thirteenth Amendment. He is also noted for his oratorical skills, having given famous speeches such as the Gettysburg Address. Lincoln had a lasting influence on U.S. political values by redefining republican values, promoting nationalism, and enlarging the powers of the federal government. His assassination, in 1865, made him a martyr for the ideal of national unity.Photo credit: Alexander Gardner