Sir Joseph Whitworth (1803-87) was arguably Britain's best ever mechanical engineer, world famous for the standard screw thread named after him, machine tool designs so innovative he pioneered a new era, and his revolutionary hexagonally led guns. He also gave the western world its first one-inch standard, taught engineers precise measurement, decimalized engineering measurement, invented mechanical street sweepers, developed the hydraulic forging press, propogated the idea of mass production, founded the Whitworth scholarships for engineering science, set up a university engineering laboratory and helped to promote the Atlantic telegraph. Many of his machines and tools were exhibited at the Great Exhibition in 1851. This biography analyzes Whitworth's engineering and gun design, and traces the development of his career in the context of his personal life and the politics of his time.