Short answers, pulled from the story.
Uncle Sam is a national personification of the United States, representing the federal government or the country as a whole. He is depicted as an elderly white man wearing a white top hat with stars on a blue band, a blue tailcoat, and red-and-white-striped trousers. The character has been a popular symbol in American culture since the early 19th century.
According to popular legend, Uncle Sam was named after Samuel Wilson, a meatpacker from Arlington, Massachusetts, who supplied rations to American soldiers during the War of 1812. However, the earliest confirmed use of the name as a metaphor for the United States dates to 1810, before Wilson held any government contract, and the story linking Wilson to the name did not appear in print until 1842.
James Montgomery Flagg created the iconic Uncle Sam recruiting poster during World War I in 1917. The image was inspired by a British recruiting poster showing Lord Kitchener in a similar pose. More than four million copies were printed between 1917 and 1918, and the image was also widely used during World War II.
The first reference to Uncle Sam in formal literature was in the 1816 allegorical book The Adventures of Uncle Sam, in Search After His Lost Honor. An earlier casual use appears in an 1810 journal entry by Isaac Mayo, a midshipman in the US Navy, suggesting the name was already common slang by that date.
Uncle Sam Day is observed on the 13th of September, the birthday of Samuel Wilson, the meatpacker associated with the origin of the Uncle Sam name. A Congressional joint resolution officially designated the 13th of September 1989, as Uncle Sam Day.
There are two memorials to Uncle Sam, both honoring Samuel Wilson. The Uncle Sam Memorial Statue is located in Arlington, Massachusetts, Wilson's birthplace. A second memorial stands in Riverfront Park in Troy, New York, near his long-term residence. Wilson is buried at Oakwood Cemetery in Troy, New York.