On March 13, 1852, Uncle Sam was featured as a cartoon character in the New York Lantern. The name is associated with Samuel Wilson, a meatpacker who provided food for the Army during the War of 1812. Wilson's barrels of meat were stamped with "U.S." for United States. Soldiers started calling the meat "Uncle Sam's."

The (unillustrated) character of Uncle Sam appeared years earlier, and was even mentioned in a 1775 verse of “Yankee Doodle,” the first national anthem of the United States!

Uncle Sam
Noun

personification, or symbol, of the United States.