Art by Marcel Duchamp

In 1917, Duchamp submitted a standard porcelain urinal, signed with the pseudonym "R. Mutt" and titled Fountain, to an exhibition that claimed to accept any work from any artist who paid the entry fee; it was rejected anyway, and the resulting controversy over what counts as art became one of the most consequential arguments in 20th-century art history. He later stepped back from making conventional art almost entirely, telling most of the world he'd given it up for chess, while secretly spending his final two decades building Étant donnés, an elaborate hidden diorama only revealed to the public after his death. He also occasionally worked and exhibited under a female alter ego, Rrose Sélavy.