Which Union general was nicknamed 'Little Mac'?

The Union general nicknamed “Little Mac” was George B. McClellan.

McClellan was a West Point graduate, engineer, and railroad executive who returned to military service when the Civil War began. He quickly impressed Union officials by organizing and training troops, especially around Washington, D.C. In November 1861, President Abraham Lincoln appointed him general-in-chief of the Union Army, and he later commanded the Army of the Potomac.

His soldiers admired him and used “Little Mac” affectionately, reflecting his close relationship with the men he trained. He was also called “the Young Napoleon,” a nickname that captured both his ambition and his reputation for careful planning. McClellan’s organizational talents were substantial, but critics argued that he was too cautious and repeatedly failed to use his numerical advantages decisively.

He commanded Union forces during the Peninsula Campaign and the 1862 Maryland Campaign, including the Battle of Antietam. Lincoln removed him from command after Antietam, and McClellan later ran unsuccessfully against Lincoln as the Democratic presidential nominee in 1864.