Alexander "Sandy" Calder was an American sculptor known both for his innovative mobiles (kinetic sculptures powered by motors or air currents) that embrace chance in their aesthetic, his static "stabiles", and his monumental public sculptures.

Calder preferred not to analyze his work, saying, "Theories may be all very well for the artist himself, but they shouldn't be broadcast to other people." His father, Alexander Stirling Calder, and grandfather, Alexander Milne Calder, were also sculptors.

In fact, it was Marcel Duchamp who coined the term “mobile” to describe Calder’s moving sculptures — a name that stuck and became one of the most recognizable forms in modern art.

His background in mechanical engineering helped him transform balance, gravity, and motion into poetry — turning physics into art.