Who invented the Why-Why Diagram?

The Why-Why Diagram, also known as the "5 Whys" technique, was popularized by Taiichi Ohno, a prominent figure in the development of the Toyota Production System. While the roots of the method can be traced back to earlier problem-solving techniques, Ohno formalized its use in the 1950s as a way to identify the root causes of problems by repeatedly asking "why" to delve deeper into the issues. This method has since become widely used in various industries for continuous improvement and root cause analysis.