Ulysses S. Grant (born Hiram Ulysses Grant HY-rəm yoo-LISS-eez; April 27, 1822 – July 23, 1885) was an American military officer and politician who served as the 18th president of the United States from 1869 to 1877. As president, Grant was an effective civil rights executive who created the Justice Department and worked with the Radical Republicans to protect African Americans during Reconstruction. Previously, as Commanding General, he led the Union Army to victory in the American Civil War in 1865 and thereafter briefly served as Secretary of War.

Raised in Ohio, Grant possessed an exceptional ability with horses. Admitted to West Point, Grant graduated 21st in the class of 1843 and served with distinction in the Mexican–American War. In 1848, he married Julia Dent, and together they had four children. Grant resigned from the army in 1854 and returned to his family but lived in poverty. He joined the Union Army after the American Civil War broke out in 1861 and rose to prominence after winning several early Union victories on the Western Theater. In 1863 he led the Vicksburg campaign, which gained control of the Mississippi River, dealing a serious strategic blow to the Confederacy, splitting it in two. President Abraham Lincoln promoted him to lieutenant general after his victory at Chattanooga. For thirteen months, Grant fought Robert E. Lee during the high-casualty Overland Campaign and at Petersburg. After Lee fled Petersburg, Grant defeated him at Appomattox. On April 9, 1865, Lee formally surrendered to Grant. A week later, Lincoln was assassinated and was succeeded by President Andrew Johnson, who promoted Grant to General of the Army in 1866. Later Grant openly broke with Johnson over Reconstruction policies; Grant used the Reconstruction Acts, which had been passed over Johnson's veto, to enforce civil rights for recently freed African Americans.

A war hero, drawn in by his sense of duty, Grant was unanimously nominated by the Republican Party and was elected president in 1868. As president, Grant stabilized the post-war national economy, supported Congressional Reconstruction, ratification of the 15th Amendment, and crushed the Ku Klux Klan. Under Grant, the Union was completely restored. He appointed African Americans and Jewish Americans to prominent federal offices. In 1871, Grant created the first Civil Service Commission, advancing civil service more than any prior president. The Liberal Republicans and Democrats united behind Grant's opponent in the presidential election of 1872, but Grant was handily re-elected. Grant's Native American policy was to assimilate Indians into the White culture; the Great Sioux War was fought during his term. Grant's foreign policy was mostly peaceful, without war, the Alabama Claims against Great Britain skillfully resolved, but his prized Caribbean Dominican Republic annexation was rejected by the Senate.

The Grant administration is traditionally known for prevalent scandals including the Gold Ring and the Whiskey Ring. However, modern scholarship has better appreciated Grant's appointed reformers and prosecutions. Grant appointed John Brooks Henderson and David Dyer, who prosecuted the Whiskey Ring. Grant appointed Benjamin Bristow and Edwards Pierrepont, who served as Grant's anti-corruption team. Grant appointed Zachariah Chandler, who cleaned up corruption in the Interior. Grant's administration prosecuted Mormon polygamists (1871), pornographers, and abortionists (1873–1877). The Panic of 1873 plunged the nation into a severe economic depression that allowed the Democrats to win the House majority. In the intensely disputed presidential election of 1876, Grant facilitated the approval by Congress of a peaceful compromise.

In his retirement, Grant was the first president to circumnavigate the world on his tour, dining with Queen Victoria and meeting many prominent foreign leaders. In 1880, Grant was unsuccessful in obtaining the Republican presidential nomination for a third term. In the final year of his life, facing severe financial reversals and dying of throat cancer, he wrote his memoirs, which proved to be a major critical and financial success. At the time of his death, he was memorialized as a symbol of national unity. Grant was a modern general and "a skillful leader who had a natural grasp of tactics and strategy". Historical assessments of his presidency have ranked him low, 38th in 1994 and 1996, but Grant has moved up in recent years, to 21st in 2018 and 20th in 2021. Although critical of scandals, modern historians have emphasized his two-term presidential accomplishments. These included the prosecution of the Klan, treatment of blacks as both human and American, an innovative Native American policy, and the peaceful settlements of the Alabama Claims and controversial 1876 presidential election.