Stephen Arnold Douglas (April 23, 1813 – June 3, 1861) was an American politician and lawyer from Illinois. He was the Democratic Party nominee for president in the 1860 election, but he was defeated by Republican candidate Abraham Lincoln. Douglas had previously bested Lincoln in the 1858 Illinois election for the United States Senate, which is known for the Lincoln–Douglas debates. During the 1850s, Douglas was one of the foremost advocates of popular sovereignty, which held that each territory should be allowed to determine whether to permit slavery within its borders. Douglas was nicknamed the "Little Giant" because he was short in physical stature, but a forceful and dominant figure in politics.

Born in Brandon, Vermont, Douglas migrated to Jacksonville, Illinois in 1833 to establish a legal practice. He experienced early success in politics as a member of the Democratic Party, serving in the Illinois House of Representatives and various other positions. He resigned from the Supreme Court of Illinois upon being elected to the United States House of Representatives in 1843. Douglas became an ally of President James K. Polk, and favored the annexation of Texas and the Mexican–American War. He was one of four Northern Democrats in the House to vote against the Wilmot Proviso, which would have banned slavery in any territory acquired from Mexico.

The Illinois legislature elected Douglas to the United States Senate in 1847, and Douglas emerged as a national party leader during the 1850s. Along with Henry Clay, he led the passage of the Compromise of 1850, which settled some of the territorial issues arising from the Mexican–American War. Douglas was a candidate for president at the 1852 Democratic National Convention, but lost the nomination to Franklin Pierce. Seeking to open the west for expansion, Douglas introduced the Kansas–Nebraska Act in 1854. Though Douglas had hoped the Kansas–Nebraska Act would ease sectional tensions, it elicited a strong reaction in the North and helped fuel the rise of the anti-slavery Republican Party. Douglas once again sought the presidency in 1856, but the 1856 Democratic National Convention instead nominated James Buchanan, who went on to win the election. Buchanan and Douglas split over the admission of Kansas as a slave state, as Douglas accused the pro-slavery Kansas legislature of having conducted an unfair election.