Uncle Sam
From Longman Dictionary of Contemporary EnglishUncle SamUncle Sam /ˌʌŋkəl ˈsæm/ noun informalSGCOUNTRY/NATION the US, or the US government, sometimes represented by the figure of a man with a white beard and tall hatOrigin Uncle Sam (1800-1900) Probably based on U.S., short for United States