Alexander Calder (1898-1976) was an American sculptor best known for inventing the mobile, a kinetic sculpture that moves with air currents. He created thousands of sculptures over his career, including both mobiles that moved and stationary sculptures called "stabiles". Some of his most famous works included "Romulus and Remus" from 1928 and the 30-ton steel sculpture "Flamingo" installed in downtown Chicago in 1973.