First attested 1812. Common folklore holds that his origins come from the men of an army base in Troy, New York, who would receive barrels of meat stamped with the initials U.S. The soldiers jokingly referred to it as the initials of the meat supplier, Uncle Samuel Wilson.
Proper noun 
- A personification of the United States government.
- Uncle Sam Needs You! means The [U.S.] Army Needs You!