Updated: Mar 28, 2019
Charlemagne (aka "Charles the Great") Standardized the Imperial measuring system based on the length of his foot. Up until that time (~800AD), measuring systems were disjointed and it created problems for trade between countries and cultures.
Although many kings had tried to standardize a measurement system prior to Charlemagne, it was Charles the Great who was able to finally get it to stick. The system is used only by three countries today Liberia, Myanmar and of course the United States of America.
The world adopted a practical measuring system (the metric system) around 1799. You may ask, "So why does the US continue using the Imperial system?"