Marcel; Uncle Sam is the uncle of all Americans. He represents the government (good or bad). The British have John Bull, other countries have other symbals I am sure. The term Uncle Sam comes from I believe the Spanish American war when all government issue items (even mules) were marked U.S. People would ask what is U.S. and someone came up with Uncle Sam. The image used here comes from a recruitment poster, he is pointing his finger at you and the words "I want you for the U.S. Army" are written below it.
