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 Commanding General, he led the Union Army to victory in the American Civil War in 1865 and thereafter briefly served as U.S. Secretary of War. Later, as president, Grant was an effective civil rights executive who signed the bill that created the Justice Department and worked with Radical Republicans to protect African Americans during Reconstruction.

Born and raised in Ohio, Grant possessed an exceptional ability with horses. Admitted to West Point, Grant graduated 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 but returned to his family impoverished. He joined the Union Army shortly after the American Civil War broke out in 1861 and rose to prominence after winning early Union victories in 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 surrounded and captured his army at Appomattox. On April 9, 1865, Lee formally surrendered to Grant. In 1866, president Andrew Johnson promoted Grant to General of the Army. 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 then elected president in 1868. As president, Grant stabilized the post-war national economy, supported congressional Reconstruction and the ratification of the Fifteenth 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, he created the first Civil Service Commission, advancing the civil service more than any prior president. The Liberal Republicans and Democrats united behind Grant's opponent in the 1872 election, but Grant was handily reelected. Grant's Native American policy was to assimilate Indians into White culture; the Great Sioux War was fought during his term. His foreign policy was mostly peaceful, without war, the Alabama Claims against Great Britain skillfully resolved. However, his prized Caribbean Dominican Republic annexation was rejected by the Senate.

The Grant administration was often remembered primarily for a number of scandals, including the Gold Ring and the Whiskey Ring, but modern scholarship has better appreciated Grant's appointed reformers and prosecutions. Grant appointed John Brooks Henderson and David Dyer, who prosecuted the Whiskey Ring; Benjamin Bristow and Edwards Pierrepont, who served as Grant's anti-corruption team; and Zachariah Chandler, who cleaned up corruption in the Interior. Grant's administration prosecuted Mormon polygamists in 1871, vice crimes such as pornography, and abortion from 1873 to 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 1876 presidential election, Grant facilitated the approval by Congress of a peaceful compromise.

With the tour he took in his retirement, Grant became the first president to circumnavigate the world, 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 were published in two volumes in 1885 and 1886, shortly after Grant's death. They 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 and rankings of Grant were negative about him and his presidency before recovering somewhat beginning in the 1980s. The consensus among them rates his presidency below average. Grant's critics take a negative view of his economic mismanagement and his failed Dominican Republic annexation treaty, while his admirers emphasize Grant's concern for Native Americans and enforcement of civil and voting rights.