The metric system is generally accepted to have been first created by Gabriel Mouton, a vicar in Lyons, France in 1670. Mouton proposed a decimal system of measurement based on the length of one minute of the arc of a great circle of the Earth (now called a nautical mile, 1852 meters). The metric system has gone through numerous revisions, including work by the French Academy of Sciences beginning in 1790 to create measures of volume as well as larger and smaller units of volume and length by multiplying or dividing by ten. Scientific surveys and international conferences continued to refine the system, the most recent being a simplification adopted in 1960 by the General Conference on Weights and Measures, an international consortium.
There have also been -- and continue to be -- political considerations in the use of the metric system. In its early years in France, the system fell into and out of favor during different points in history, until it was finally adopted once and for all in 1840. Here in the U.S., Congress has been reluctant to require its use because of the preference of most American for the inch-pound system. However, as trade has become more global in nature, U.S. companies have needed to adopt the metric system to remain relevant in international commerce.
There is a detailed account of the history of the metric system on the website of the U.S. Metric Association, which also has puzzles that can help familiarize students with metric measurements.