Gordon Granger (November 6, 1821 – January 10, 1876) was a career U.S. Army officer, and a Union general during the American Civil War, where he distinguished himself at the Battle of Chickamauga.

Granger is best remembered for his part in the Battle of Chickamauga and the Battle of Chattanooga and for issuing General Order No. 3 on June 19, 1865, in Galveston, Texas, further informing residents of, and enforcing, Abraham Lincoln's Emancipation Proclamation which set all Confederate states' slaves free on January 1, 1863. Since 2021, June 19 has been commemorated by the federal holiday of Juneteenth.

Granger was born in Joy, Wayne County, New York, in 1821 to Gaius Granger and Catherine Taylor being one of three children in his family. His mother died on April 17, 1825, one month after giving birth to a daughter. His father married again in November 1826 to Sara (Salley) Emery and the two would have 10 children. He spent his early years with his paternal grandparents (Elihu and Apema or Apama Granger) in Phelps, New York. While attending high school he developed health issues which carried on throughout his life He was a teacher in North Rose, New York prior to entering the United States Military Academy.

Granger was appointed to the academy in 1841 when he was 19 years old. While there he met John Pope who later became one of his mentors. It is possible that his grudge with Ulysses S. Grant started when he was there with Grant holding the grudge more than Granger. He graduated from the United States Military Academy in 1845 placed thirty-fifth in a class of forty-one cadets. He was commissioned a brevet second lieutenant and assigned to the Second Infantry Regiment stationed in Detroit, Michigan. In July 1846 he transferred to the newly constituted Regiment of Mounted Riflemen at Jefferson Barracks, Missouri.

During the Mexican–American War, Granger fought in Winfield Scott's army. He took part in the Siege of Veracruz, the Battle of Cerro Gordo, the Battle of Contreras, the Battle of Churubusco, and the Battle for Mexico City. Granger received two citations for gallantry and in May 1847 received his regular commission as a second lieutenant. After the war, he served on the western frontier in Oregon and then Texas. In 1853 he became a first lieutenant.

When the Civil War started, Granger was on sick leave. He was temporarily assigned to the staff of General George B. McClellan in Ohio. After recovering, he transferred back to the Regiment of Mounted Riflemen where he was promoted to captain in May 1861. As an adjutant of General Samuel D. Sturgis he saw action at the Battle of Dug Springs and observed the Union defeat at Wilson's Creek in August 1861 in Missouri, serving as a staff officer to General Nathaniel Lyon. Granger was cited for gallantry at Wilson's Creek, became a brevet major and was made a commander of the St. Louis Arsenal.

In November 1861, Granger assumed command of the 2nd Michigan Cavalry Regiment at Benton Barracks in St. Louis, becoming a colonel of volunteers. One of the Union veterans wrote in a memoir that Granger's "military genius soon asserted itself by many severe lessons to the volunteer officers and men of this regiment. He brought them up to the full standard of regulars within a period of three months," and "though a gruff appearing man, had succeeded in winning the respect of his regiment by his strict attention to all the details of making a well disciplined body of soldiers out of a mass of awkward men from every walk of life."

In February 1862, on the orders of General John Pope, the 2nd Michigan proceeded from St. Louis to Commerce, Missouri, where Pope assembled nearly 20,000 Union troops for an advance on New Madrid, Missouri. Granger assumed command over the Third Cavalry Brigade consisting of the 2nd and the 3rd Michigan cavalry regiments. After the 7th Illinois joined the brigade, it was reorganized into a cavalry division.