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. Its actual origin is obscure. Uncle Sam represents a manifestation of patriotic emotion.

The first use of Uncle Sam in formal literature (as distinct from newspapers) was in the 1816 allegorical book "The Adventures of Uncle Sam in Search After His Lost Honor" by Frederick Augustus Fidfaddy, Esq. An Uncle Sam is mentioned as early as 1775, in the original "Yankee Doodle" lyrics of the American Revolutionary War. It is not clear whether this reference is to Uncle Sam as a metaphor for the United States, or to an actual person named Sam. The lyrics as a whole celebrate the military efforts of the young nation, besieging the British at Boston. The 13th stanza is:

Old Uncle Sam come there to change
Some pancakes and some onions,
For 'lasses cakes, to carry home
To give his wife and young ones.

The earliest known personification of 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 Uncle Sam finally appeared after the War of 1812.

However, according to an article in the 1893 The Lutheran Witness, Uncle Sam was simply another name for Brother Jonathan:

"When we meet him in politics we call him Uncle Sam; when we meet him in society we call him Brother Jonathan. Here of late Uncle Sam alias Brother Jonathan has been doing a powerful lot of complaining, hardly doing anything else." (sic)

...
Wikipedia