This paper, written on the occasion of the posthumous presentation of the Horning Memorial Award to Clessie L. Cummins, traces Cummins' contributions to the development of the high-speed diesel engine from 1920 to his death. Cummins' first engine was a single cylinder one which developed 6 hp at 600 rpm. The last, while associated with Cummins Engine Co., was the Model A rated 85 hp at 2200 rpm. The author highlights various steps between these two engines, including race car, automobile, locomotive, and truck applications.The last half of the paper describes in detail Cummins' last engine: one run on natural gas by spark ignition. It is a 4-cycle, 3-cyl, barrel type with a design rating of 125 hp at 3000 rpm.