George B. McClellan (1826-1885) was a U.S. Army officer, railroad president and politician who served as a major general during the Civil War (1861-65). McClellan organized the Army of the Potomac in 1861 and briefly served as general-in-chief of the Union Army. McClellan was well liked by his men, but his reticence to attack the Confederacy with the full force of his army—despite a significant numerical advantage—put him at odds with President Abraham Lincoln. In 1862, McClellan’s Peninsula Campaign unraveled after the Seven Days Battles, and he also failed to decisively defeat Robert E. Lee’s Confederate Army at the Battle of Antietam later that year. Frustrated by McClellan’s overly cautious tactics, Lincoln removed him from command of the Army of the Potomac in late 1862. McClellan would go on to mount a failed presidential campaign against Lincoln in 1864, and would later serve as the governor of New Jersey from 1878 to 1881.