James Montgomery Flagg provided the face while Waltr Botts provided the pose. Original idea taken from the british used in recruting for WWI and WWII in the USA.
The 87th United States Congress adopted the following resolution on September 15, 1961: "Resolved by the Senate and the House of Representatives that the Congress salutes Uncle Sam Wilson of Troy, New York, as the progenitor of America's National symbol of Uncle Sam."
ref:
http://en.wikipedia.org/wiki/Uncle_Sam