Since the early 19th century, Uncle Sam has been a popular symbol of the U.S. government in American culture and a manifestation of patriotic emotion.
[3] Uncle Sam has also developed notoriety for his appearance in military propaganda, popularized by a 1917 World War I recruiting poster by James Montgomery Flagg.
A March 24, 1810, journal entry by Isaac Mayo (a midshipman in the US Navy) states: weighed anchor stood down the harbor, passed Sandy Hook, where there are two light-houses, and put to sea, first and the second day out most deadly seasick, oh could I have got onshore in the hight [sic] of it, I swear that uncle Sam, as they call him, would certainly forever have lost the services of at least one sailor.
[10]An 1810 edition of Niles' Weekly Register has a footnote defining Uncle Sam as "a cant term in the army for the United States.
[13] Additionally, the earliest known mention definitely referring to the metaphorical Uncle Sam is from 1810, predating Wilson's contract with the government.
Flagg's depiction of Uncle Sam was shown publicly for the first time, according to some, on the cover of the magazine Leslie's Weekly on July 6, 1916, with the caption "What Are You Doing for Preparedness?
Flagg's image was also used extensively during World War II, during which the US was codenamed "Samland" by the German intelligence agency Abwehr.
A Congressional joint resolution[23] designated September 13, 1989, as "Uncle Sam Day", the birthday of Samuel Wilson.