Originally published as the cover for the July 6, 1916, issue of Leslie's Weekly with the title "What Are You Doing for Preparedness?" this portrait of "Uncle Sam" went on to become--according to its creator, James Montgomery Flagg--"the most famous poster in the world." Over four million copies were printed between 1917 and 1918, as the United States entered World War I and began sending troops and matériel into war zones.