“He hears a loudspeaker / Call him well-known,” W. H. Auden wrote in a poem toward the end of his life. “But knows himself no better.” Fame, Auden was suggesting, can be an enigma for the famous. Your admirers assume that they know who you are, but the artist, to remain creatively alive, must keep asking questions. I thought a lot about Alexander Calder’s confrontations with fame as I worked on the second and final volume of my biography of the pathbreaking American sculptor; he was 78 when he died, in 1976.

What I discovered—what often surprised me—was how frequently Calder challenged assumptions about what a sculpture by Calder ought to be. Although a charming, voluble, and highly social man, Calder by and large preferred to let his work speak for itself. But a biographer develops a sixth sense for an artist’s thinking, and during the dozen years I spent looking at Calder’s life I became convinced that the ruptures and leaps that characterized his work were fueled by a desire to shake up his own assumptions—as well as those of his admirers. I think that’s what Calder was doing when, mere months after his enormously popular 1943 Museum of Modern Art retrospective, he produced works made of discrete elements cast in bronze, the elements to be balanced one on top of the other so that this ancient and earthbound material suddenly moved. For Calder, who was already recognized as a master of mobiles that looked as light as air, this embrace of the heaviness of bronze was a way of upending his own accomplishment. By mobilizing bronze, he made the known suddenly, thrillingly unknown.