Arguably the most influential twentieth-century artist. Picabia, Delaunay and Léger were members of his brothers’ (Villon and Duchamp-Villon) discussion-group. Apollinaire, a close friend, wrote about his work, and crossed France with him in Picabia’s fast car. Stella went to buy the famous urinal with him; Brancusi entrusted him with selling his work; Man Ray filmed his wedding. Varèse and Williams were among his earlier friends in New York. He edited ‘VVV’ with Breton and Ernst, coined the term ‘mobile’ for Calder, and taught Cage chess. Tinguely met him in a Paris bistro, Hamilton collaborated on a classic remake.