 George Brinton McClellan (December 3, 1826 – October 29, 1885) was an American soldier, civil engineer, railroad executive, and politician. A graduate of West Point, McClellan served with distinction during the Mexican-American War, and later left the Army to work in railroads until the outbreak of the American Civil War. Early in the war, McClellan was appointed to the rank of major general and played an important role in raising a well-trained and organized army, which would become the Army of the Potomac; he served a brief period (November 1861 to March 1862) as general-in-chief of the Union Army. Although McClellan was meticulous in his planning and preparations, these very characteristics hampered his ability to challenge aggressive opponents in a fast-moving battlefield environment. He chronically overestimated the strength of enemy units and was reluctant to apply principles of mass, frequently leaving large portions of his army unengaged at decisive points.
