James Montgomery Flagg (June 18, 1877 – May 27, 1960)

found at http://www.britannica.com/EBchecked/topic/617597/The-United-States-Army

"I Want You for the U.S. Army" 1917

This is perhaps the single most iconic poster ever created in America. Every American is familiar with the image, and it was used to recruit members for both world wars. For many Americans, Uncle Sam represents the very spirit of patriotism, and the character has even been immortalized in a number of comic books by DC comics, such as the "Freedom Fighters"

While James Flagg himself may not be as much of a household word as Norman Rockwell or some other American artists, the image he produced easily trumps them.