"Doughboy" was a term used for American soldiers in World War I, in particular the soldiers of the American Expeditionary Forces. There are many theories about the origins of the word doughboy to describe soldiers, including some going back to the Mexican American War. 

Images of doughboys were used throughout the war to inspire patriotism. This poster, showing a fierce-looking doughboy standing over a dead German soldier, is encouraging Americans to buy Liberty Bonds to support the war effort.