French engineer who originated the principle of the four-stroke internal-combustion engine. His achievement lay partly in his emphasizing the previously unappreciated importance of compressing the fuel–air mixture before ignition.

Beau de Rochas patented his idea in 1862 but did not build such an engine, leaving the development to others. As a result of the work of Nikolaus A. Otto of Germany and Étienne Lenoir of France, four-stroke engines almost completely displaced all other types of internal combustion engines and came into universal use.