Walter A. Shewhart

Walter Andrew Shewhart was an American physicist, engineer and statistician who spent his career at Western Electric and Bell Telephone Laboratories. On 16 May 1924 he wrote an internal Bell Labs memo introducing the control chart, a tool for distinguishing ordinary process variation from a genuine, correctable problem, building it to help reduce failures in buried telephone equipment that was costly to repair. The distinction he drew between common-cause and special-cause variation became the foundation of statistical process control and, later, of Six Sigma. Shewhart also mentored W. Edwards Deming at Bell Laboratories, and the plan-do-check-act improvement cycle used across quality management is sometimes called the Shewhart cycle in his honor.