George Brinton McClellan was born on December 3, 1826, into an affluent family in Philadelphia, Pennsylvania.

A studious child, McClellan made the decision to enter military service at age 15 and was accepted to West Point despite being several months shy of the age requirement of 16. McClellan ranked second in his class upon graduation from West Point in 1846.

McClellan was commissioned as a brevet second lieutenant in the Army Corps of Engineers, and played an active part in the Mexican-American War. As an engineering officer, McClellan frequently saw combat and was promoted to the rank of captain for showing gallantry under fire.

He returned to West Point after the war and continued to serve as an engineer for three years before being transferred to the western frontier. McClellan’s intelligence and ambition caught the eye of the future president of the Confederate States of America, Jefferson Davis—then the U.S. secretary of war—who in 1855 secured him an appointment to travel to Europe to study military tactics being used in the Crimean War.

McClellan left the military in 1857 and became chief engineer of the newly constructed Illinois Central Railroad. By 1860, he had become president of the Ohio and Mississippi River Railroad, headquartered in Cincinnati.

During this time, McClellan met and wed Mary Ellen Marcy, the daughter of one of his former commanders. The couple would go on to have two children: Mary “May” McClellan and George B. McClellan Jr.

Like many people at the time, McClellan opposed the outright abolition of slavery, though he was committed to the preservation of the Union.

At the outbreak of the Civil War in 1861, he accepted command of the volunteer army of the state of Ohio. His skill at training the Ohio Volunteers won him favor in Washington, and he was soon promoted to the rank of major general in the regular army.

In the spring and summer of 1861, McClellan won a series of small battles in western Virginia and gained the nickname “The Young Napoleon.”

But after the sobering Union defeat at the First Battle of Bull Run under the command of Brigadier General Irvin McDowell, McClellan was called to Washington and given command of forces that he organized into the famed Army of the Potomac.

McClellan once again demonstrated his skill at marshalling his troops into a solid fighting unit, and his early command was marked by a period of high morale. By November 1861, McClellan had assembled an army of 168,000 troops and fortified the capital of Washington, D.C.

That same month, McClellan succeeded Winfield Scott as general-in-chief of the Union Army. Despite having assembled a massive fighting force, McClellan was wary of the Confederate Army—which he believed, through faulty intelligence, to be much stronger than it actually was—and was reluctant to mount a mass offensive.

His inaction annoyed President Abraham Lincoln and newly appointed Secretary of War Edwin Stanton, and in January 1862 they issued a general order instructing the Army of the Potomac to move south into Confederate territory. Lincoln removed McClellan as general-in-chief in March of 1862, stating that McClellan needed to focus his full attention on an attack on the South.

Lincoln preferred an overland campaign toward Richmond, but McClellan proposed an amphibious maneuver in which the Union Army would land on the Virginia Peninsula, effectively circumventing the rebels under General Joseph E. Johnston.

McClellan put his Peninsula Campaign into action in March 1862, landing over 120,000 men on the coast and proceeding east toward the Confederate capital. The Confederates withdrew toward Richmond, and McClellan’s troops fought their way to within only a few miles of the city.

Despite his strong position, McClellan failed to capitalize on his tactical advantage, once again believing that he might be outnumbered. When General Robert E. Lee took control of Confederate forces on June 1, he launched a series of bold offensives that culminated in the Seven Days Battles.

Furious at Lincoln’s refusal to send him reinforcements, McClellan retreated to the base of the James River, at which point his army was ordered to return to Washington.

Aggravated at what he saw as indecisiveness on the part of McClellan, Lincoln had grown dissatisfied with his most famous general. But after Lee scored a decisive victory at the Second Battle of Bull Run in August 1862, he grudgingly called McClellan back into action in defense of Washington.

Lee soon mounted an invasion of the North during the Maryland Campaign, and in September 1862 McClellan’s forces engaged the Confederates at the Battle of Antietam. After McClellan’s forces succeeded in breaching the Confederate lines, he once again stalled, keeping over a third of his army in reserve and allowing Lee to retreat into Virginia.

The Battle of Antietam was the single bloodiest day of combat in the Civil War, and while it was presented as a Union victory in the Northern press, it was in effect a tactical draw. Frustrated that McClellan had again failed to destroy Lee’s army, Lincoln officially removed him from command in November 1862.

In 1864, the Democratic Party nominated McClellan to run against Lincoln for the presidency. His campaign was marred by a schism that split the Democratic vote along pro- and anti-war lines.

A staunch “War Democrat” committed to the preservation of the Union, McClellan was forced to battle elements of his own party in addition to Lincoln, and he was easily beaten.

Following his presidential defeat, McClellan resigned from the army and spent several years in Europe. He would return to the railroad business in 1872 as president of the Atlantic and Great Western Railroad.

From 1878 to 1881, he served one term as the governor of New Jersey. McClellan’s later years were spent writing a memoir called McClellan’s Own Story, which was published after his 1885 death at the age of 58.