Uncle Sam is a common national personification of the American government originally used during the War of 1812. He is depicted as a stern elderly man with white hair and a goatee beard. Typically he is dressed in clothing that recalls the design elements of flag of the United States—for example, a top hat with red and white stripes and white stars on a blue band, and red and white striped trousers. The first use of Uncle Sam in literature was in the 1816 allegorical book The Adventures of Uncle Sam in Search After His Lost Honor by Frederick Augustus Fidfaddy, Esq.

Earlier representative figures of the United States included such beings as "Brother Jonathan," used by Punch magazine. These were overtaken by Uncle Sam somewhere around the time of the Civil War. The female personification "Columbia" has seldom been seen since the 1920s. The well-known "recruitment" image of Uncle Sam was created by James Montgomery Flagg, an illustrator and portrait artist best known for commercial art. The image of Uncle Sam was shown publicly for the first time, according to some, in a picture by Flagg on the cover of the magazine Leslie's Weekly, on July 6, 1916, with the caption "What Are You Doing for Preparedness?" More than four million copies of this image were printed between 1917 and 1918. The image also was used extensively during World War II.

The name originated from meat packer Samuel Wilson (1766-1854) of Troy, New York who stamped meat which was going to American soldiers in the War of 1812 "US" for United States. First drawn as an elderly man with a goatee, noted political cartoonist Thomas Nast (1840-1902) refined his image in the 1870s to include a top hat and a stars and stripes costume which we recognize today.

Illustrator James Montgomery Flagg (1877-1960) first painted his iconic image of Uncle Sam pointing toward the viewer for the July 6, 1916 cover of Leslie's Weekly Magazine. The painting was then used as a WWI recruiting poster with text at the bottom "I Want You For U.S. Army" in 1917. Flagg used himself as a model for Uncle Sam. Four million posters were printed, making the poster the most famous in history. The poster was used again in WWII.

The 87th U.S. Congress adopted a resolution on September 15, 1961, crediting Samuel Wilson with the origination of Uncle Sam.

Quality Comics published eight issues of Uncle Sam Quarterly between Autumn, 1941 and Fall, 1943 and DC published two issues of Uncle Sam in 1997.