George Brinton McClellan (December 3, 1826 – October 29, 1885) was an American military officer, politician, and engineer who served as the 24th governor of New Jersey from 1878 to 1881 and as Commanding General of the United States Army from November 1861 to March 1862. He was also chief engineer and vice president of the Illinois Central Railroad, and later president of the Ohio and Mississippi Railroad in 1860.
A West Point graduate, McClellan served with distinction during the Mexican–American War. He was a railway executive and engineer until the outbreak of the American Civil War in 1861. Early in the conflict, McClellan was appointed to the rank of major general and played an important role in raising the Army of the Potomac, which served in the Eastern Theater.
McClellan organized and led the Union Army in the Peninsula campaign in southeastern Virginia from March through July 1862. It was the first large-scale offensive in the Eastern Theater.