The Oyster was the world’s first watertight watch developed by Hans Wilsdorf in 1926. Combined with a self-winding or automatic movement that could generate power from the wearer’s wrist movements alone, the need for manual winding and extracting the crown from the case would be eliminated. In 1931, the Rolex team perfected and patented the bi-directional oscillating mass, or rotor, and the Rolex Oyster Perpetual was born.