William Tecumseh Sherman (/tɪˈkʌmsə/ tih-KUM-sə; February 8, 1820 – February 14, 1891) was an American soldier, businessman, educator, and author. He served as a general in the Union Army during the American Civil War (1861–1865), earning recognition for his command of military strategy but criticism for the harshness of his scorched-earth policies, which he implemented in his military campaign against the Confederate States. British military theorist and historian B. H. Liddell Hart declared that Sherman was "the most original genius of the American Civil War" and "the first modern general".

Born in Lancaster, Ohio, into a politically prominent family, Sherman graduated in 1840 from the United States Military Academy at West Point. In 1853, he interrupted his military career to pursue private business ventures, without much success. In 1859, he became superintendent of the Louisiana State Seminary of Learning & Military Academy, now Louisiana State University, but resigned when Louisiana seceded from the Union. Sherman commanded a brigade of volunteers at the First Battle of Bull Run in 1861, and then was transferred to the Western Theater. He was stationed in Kentucky, where his pessimism about the outlook of the war led to a breakdown that required him to be briefly put on leave. He recovered and forged a close partnership with General Ulysses S. Grant. Sherman served under Grant in 1862 and 1863 in the Battle of Fort Henry and the Battle of Fort Donelson, the Battle of Shiloh, the campaigns that led to the fall of the Confederate stronghold of Vicksburg on the Mississippi River, and the Chattanooga campaign, which culminated with the routing of the Confederate armies in the state of Tennessee.

In 1864, when Grant went east to serve as the General-in-Chief of the Union Armies, Sherman succeeded him as the commander in the Western Theater. He led the capture of the strategic city of Atlanta, a military success that contributed to the re-election of President Abraham Lincoln. Sherman's subsequent famous "March to the Sea" through Georgia and the Carolinas involved little fighting but large-scale destruction of military and civilian infrastructure, a systematic policy intended to undermine the ability and willingness of the Confederacy to continue fighting. Sherman accepted the surrender of all the Confederate armies in the Carolinas, Georgia, and Florida in April 1865, but the terms that he negotiated were considered too generous by U.S. Secretary of War Edwin Stanton, who ordered General Grant to modify them.

When Grant became President of the United States in March 1869, Sherman succeeded him as Commanding General of the Army. Sherman served in that capacity from 1869 until 1883 and was responsible for the U.S. Army's engagement in the Indian Wars. He steadfastly refused to be drawn into party politics. In 1875, he published his memoirs, which became one of the best-known first-hand accounts of the Civil War.

Sherman was born in 1820 in Lancaster, Ohio, near the banks of the Hocking River. His father, Charles Robert Sherman, a lawyer who was a justice on the Ohio Supreme Court, died unexpectedly of typhoid fever in 1829. His widow, Mary Hoyt Sherman, remained with eleven children and no inheritance. Nine-year-old Sherman was raised by a Lancaster neighbor and family friend, attorney Thomas Ewing. Ewing was a prominent member of the Whig Party who became U.S. senator for Ohio and the first Secretary of the Interior. Sherman was a fifth cousin three times removed of US founding father Roger Sherman.

Sherman's older brother Charles Taylor Sherman became a federal judge. One of his younger brothers, John Sherman, was one of the founders of the Republican Party and served as a U.S. Representative, Senator, and cabinet secretary. Another younger brother, Hoyt Sherman, was a successful banker. Two of his foster brothers served as major generals in the Union Army during the Civil War: Hugh Boyle Ewing, later an ambassador and author, and Thomas Ewing Jr., who was a defense attorney in the military trials of the Lincoln conspirators. Sherman's niece, Euthanasia Sherman Meade, was a pioneering woman physician in California.

Sherman's unusual given name has always attracted attention. One 19th-century source, for example, states that "General Sherman, we believe, is the only eminent American named from an Indian chief". According to Sherman's Memoirs, he was named William Tecumseh because his father had "caught a fancy for the great chief of the Shawnees, 'Tecumseh'". However, Lloyd Lewis's 1932 biography claimed that Sherman was originally named only Tecumseh and that he acquired the name William at the age of nine or ten, when he was baptized as a Catholic at the behest of his foster family. According to Lewis's account, which was repeated by later authors, Sherman was baptized in the Ewing home by a Dominican priest who found the pagan name Tecumseh unsuitable and instead named the child William after the saint on whose feast day the baptism took place. Sherman had already been baptized as an infant by a Presbyterian minister and recent biographers believe, contrary to Lewis's claims, that he was probably given the first name William at that time. As an adult, Sherman signed all his correspondence, including to his wife, "W. T. Sherman". His friends and family called him Cump.

Senator Ewing secured an appointment for the 16-year-old Sherman as a cadet in the United States Military Academy at West Point. Sherman roomed with and befriended another important future Civil War general for the Union, George Henry Thomas. Sherman excelled academically at West Point, but he treated the demerit system with indifference. Fellow cadet William Rosecrans remembered Sherman as "one of the brightest and most popular fellows" at the academy and as "a bright-eyed, red-headed fellow, who was always prepared for a lark of any kind". About his time at West Point, Sherman says only the following in his Memoirs: