The first Cadillac automobiles were built in the last quarter, 1902; they were 2-seater "horseless carriages" powered by a reliable and sturdy 10 hp (7 kW) single-cylinder engine developed by Henry Martyn Leland and built by Leland and Faulconer Manufacturing Company of Detroit, of which Henry Leland was founder, vice-president and general manager.
Reformed as the Cadillac Automobile Company in August 1902, it began manufacturing the runabouts and named them "Cadillac" after the city's founder Antoine Laumet, the self-styled Antoine Laumet de La Mothe, sieur de Cadillac. This early "letter model" naming system was used from late 1902 (often considered 1903s) to 1908.
All single-cylinder Cadillacs share many parts in common. In fact, the Models E, F, K, M, S, and T are essentially the same vehicle with different bodies.
Source: Wikipedia, 2011