A leader of the Dada movement that emerged in Europe and America during World War I, Marcel Duchamp assaulted the traditional concept of art as a unique, physical object distinguished by superior handwork or craftsmanship. In its place he proposed that the central, animating principle of art should be the idea. His reputation as the century's most controversial artist began with the public's riotous reaction to his Nude Desending a Staircase at the 1913 Armory Show. That same year he created his first "ready-made" by attaching a bicycle wheel to a kitchen stool. In 1917, he exhibited a urinal under the title Fountain, and in 1919, he created his infamous L.H.O.O.Q. by adding a goatee over a printed reproduction of the Mona Lisa. Often adding inscriptions with humorous puns and ironic double meanings to his works, Duchamp raised philosophical speculation to a higher level of importance than the physical object. Shocked by his unconventional tactics, critics labeled his works"anti-art."