Alexander Calder's work first appeared in the Museum of Modern Art's galleries in 1930, in the exhibition Painting and Sculpture by Living Americans. Calder cultivated friendships and working relationships with notable figures, including Alfred H. Barr Jr., the Museum's founding director, and James Johnson Sweeney, with whom he collaborated on his retrospective exhibition in 1943. His work is imprinted on MoMA's early history, not only for its material and conceptual innovation but also for its presence at significant moments, such as a mobile made to hang over the lobby's grand staircase on the occasion of the new Goodwin and Stone building (Lobster Trap and Fish Tail, which hangs there to this day); a candelabra to adorn the tables at a celebratory anniversary event; and a sculpture to fly off a flagpole to advertise the landmark exhibition Cubism and Abstract Art.