Uncle Sam is less of a who, and more of a what. You see during World War II, the government needed people tp pitch in with the war effort. This meant everything from young men enlisting, women volunteering at USO club, and ofcourse people buying war bonds to fund the war. So the government decided to put a friendly face on the effort. Hence was the creation of the totally ficticious Uncle Sam. Ofcourse over the past 70 years since the war, Uncle Sam has become such an iconic figure in our culture (both in America and around the world) that most people truly believe that the man in the picture that we all know and love, was indeed someones uncle. Well I hope that helps. Please keep reading and asking questions. God Bless.