He was known for his readymades such as "L.H.O.O.Q.", a copy of the "Mona Lisa" with a penciled-in mustache & beard
[DOC] [TLE] L.H.O.O.Q, Mona Lisa with moustache, 1919 - Marcel Duchamp ... [PAR] L.H.O.O.Q, Mona Lisa with moustache, 1919 by Marcel Duchamp.