William David Coolidge (October 23, 1873 - February 3, 1975) was an American physicist. He was the director of the General Electric Research Laboratory and a vice-president of the corporation. He developed ductile tungsten, which could be more easily drawn into filaments, by purifying tungsten oxide. In 1913 he invented the Coolidge tube, an X-ray tube with an improved cathode for use in X-ray machines that allowed for more intense visualization of deep-seated anatomy and tumors. The Coolidge tube, which also utilized a tungsten filament, was a major development in the then-nascent medical specialty of radiology, and its basic design is still in use. In 1975 he was elected to the National Inventors Hall of Fame, shortly before his death at age 101.