Abraham Lincoln (February 12, 1809 – April 15, 1865) was the 16th president of the United States, serving from 1861 until his assassination in 1865. He led the United States through the American Civil War, defeating the Confederate States and playing a major role in the abolition of slavery.

Lincoln was born into poverty in Kentucky and raised on the frontier. He was self-educated and became a lawyer, Illinois state legislator, and U.S. representative. Angered by the Kansas–Nebraska Act of 1854, which opened the territories to slavery, he became a leader of the new Republican Party. He reached a national audience in the 1858 Senate campaign debates against Stephen A. Douglas. Lincoln won the 1860 presidential election, prompting a majority of slave states to begin to secede and form the Confederate States. A month after Lincoln assumed the presidency, Confederate forces attacked Fort Sumter, starting the Civil War.

As a moderate Republican, Lincoln had to navigate conflicting political opinions from contentious factions during the war effort. Lincoln closely supervised the strategy and tactics in the war effort, including the selection of generals, and implemented a naval blockade of Southern ports. He suspended the writ of habeas corpus in April 1861, an action that Chief Justice Roger Taney found unconstitutional in Ex parte Merryman, and he averted war with Britain by defusing the Trent Affair. On January 1, 1863, he issued the Emancipation Proclamation, which declared the slaves in the states "in rebellion" to be free. On November 19, 1863, he delivered the Gettysburg Address, which became one of the most famous speeches in American history. He promoted the Thirteenth Amendment to the U.S. Constitution, which, in 1865, abolished chattel slavery. Re-elected in 1864, he sought to heal the war-torn nation through Reconstruction.

On April 14, 1865, five days after the Confederate surrender at Appomattox, Lincoln was attending a play at Ford's Theatre in Washington, D.C., when he was fatally shot by Confederate sympathizer John Wilkes Booth. Lincoln is remembered as a martyr and a national hero for his wartime leadership and for his efforts to preserve the Union and abolish slavery. He is often ranked in both popular and scholarly polls as the greatest president in American history.

Lincoln was born into poverty on February 12, 1809, in a log cabin on Sinking Spring Farm near Hodgenville, Kentucky. The second child of Thomas Lincoln and Nancy Hanks Lincoln, he was a descendant of Samuel Lincoln, an Englishman who migrated to Massachusetts in 1638, and of the Harrison family of Virginia. His paternal grandfather and namesake, Captain Abraham Lincoln, moved the family from Virginia to Kentucky. The captain was killed in a Native American raid in 1786. The family settled in Hardin County, Kentucky, in the early 1800s. Nancy is widely assumed to have been the daughter of Lucy Hanks. Thomas and Nancy married on June 12, 1806, and moved to Elizabethtown, Kentucky. They had three children: Sarah, Abraham, and Thomas; Thomas died as an infant.

Lincoln's father bought multiple farms in Kentucky but could not get clear property titles to any, losing hundreds of acres in legal disputes. In 1816, the family moved to Indiana, where land titles were more reliable. They settled on a forested plot in Little Pigeon Creek Community. In Kentucky and Indiana, Thomas worked as a farmer, cabinetmaker, and carpenter. At various times, he owned farms, livestock, and town lots, appraised estates, and served on county patrols. Thomas and Nancy were members of a Separate Baptist Church, a pious evangelical group whose members largely opposed slavery. Overcoming financial challenges, Thomas obtained clear title to 80 acres (32 ha) in Little Pigeon Creek Community in 1827.

On October 5, 1818, Nancy died from milk sickness, leaving 11-year-old Sarah in charge of the household, which included her father, 9-year-old Abraham, and Nancy's 19-year-old orphan cousin, Dennis Hanks. Thomas married Sarah Bush Johnston, a widow with three children of her own, on December 2, 1819. Abraham became close to his stepmother and called her "Mama". On January 20, 1828, Lincoln's sister died in childbirth, devastating him.

Lincoln was largely self-educated. His formal schooling was from itinerant teachers. It included two short stints in Kentucky, where he learned to read, but probably not to write. After moving to Indiana at age seven, he attended school only sporadically, for a total of less than 12 months by age 15. Nonetheless, he was an avid reader and retained a lifelong interest in learning.