Uncle Sam

Uncle Sam (initials U.S.) is a common national personification of the American government or the United States in general that, according to legend, came into use during the War of 1812 and was supposedly named for Samuel Wilson but whose actual origin may be obscure. Uncle Sam represents a manifestation of patriotic emotion (of people in America for the country in which they live).

Evolution
The term Uncle Sam is reputedly derived from Samuel Wilson, a meat packer fromTroy, New York, who supplied rations for the soldiers during the war of 1812. There was a requirement at the time for contractors to stamp their name and where the rations came from onto the food they were sending. Wilson's packages were labeled "E.A – US." When someone asked what that stood for, a coworker joked and said "Elbert Anderson (the contractor) and Uncle Sam," referring to Sam Wilson, though it actually stood for United States. Doubts have been raised as to this being the source of the term as the claim as to Samuel Wilson did not appear in print until 1842. Additionally, the earliest reference found to date of the term in 1810 predates Wilson's contract with the government. As early as 1835 Brother Jonathan made a reference to Uncle Sam implying that they symbolized different things: Brother Jonathan was the country itself while Uncle Sam was the government and its power.

Uncle Sam didn't get a standard appearance until the well-known "recruitment" image of Uncle Sam was created by James Montgomery Flagg (inspired by a British recruitment poster showing Lord Kitchener in a similar pose). It was this image more than any other that set the appearance of Uncle Sam as the elderly man with white hair and a goatee wearing a white top hat with white stars on a blue band, a blue tail coat and red and white striped trousers.

Earlier personifications.

The earliest known personification of what would become the United States was "Columbia" who first appeared in 1738 and sometimes was associated with Liberty.

With the American Revolutionary War came "Brother Jonathan" as another personification and finally after the War of 1812 Uncle Sam appeared.

While Columbia had appeared with either Brother Jonathan or Uncle Sam, her use as personification for the U.S. had declined in favor of liberty, and once she became the mascot of Columbia the 1920s, she was effectively abandoned.

taken from:

https://en.wikipedia.org/wiki/Uncle_Sam