Abraham Lincoln and George B. McClellan in the general's tent

George B. McClellan (1826–1885) was a U.S. Army officer, civil engineer, and politician, best known for his role as a major general during the American Civil War. Born in Philadelphia, Pennsylvania, McClellan graduated from the U.S. Military Academy at West Point in 1846 and served in the Mexican-American War before working as a railroad executive.

During the Civil War, McClellan was appointed as the commander of the Army of the Potomac in 1861. He is often remembered for his organizational skills and ability to train a large, effective army. However, McClellan was criticized for his cautiousness and reluctance to engage Confederate forces decisively. His hesitancy, especially during the Peninsular Campaign and the Battle of Antietam, led to tensions with President Abraham Lincoln, who sought more aggressive action.

McClellan was relieved of command in 1862 after failing to pursue General Robert E. Lee’s Confederate army more aggressively. He later ran for president in 1864 as a Democrat, but was defeated by Lincoln in the election. After the war, McClellan served as governor of New Jersey from 1878 to 1881. While McClellan's legacy as a military leader is mixed, his contributions to the organization of the Union Army were significant, and his cautious approach reflected the challenges of leading a nation through a devastating war.