The Diamond T Motor Car Company was an American truck manufacturer founded in 1905 in Chicago, renowned for combining industrial robustness with high quality finishes, earning it the nickname "The Cadillac of Trucks." During the 1920s and 1930s, it produced highly regarded commercial models such as the Diamond T Model 80, a refined-styled light pickup; the Diamond T Model 201, widely used in light commercial applications; and the Diamond T Model 301, which covered the medium duty segment. During World War II, it became a key supplier to the U.S. Army, notably producing the Diamond T 509 and the Diamond T M3 Half-Track, the latter being one of the most important armored vehicles of the conflict. In the postwar period, it launched modern and powerful lines such as the Diamond T 700 Series and the Diamond T 900 Series, geared toward long-haul heavy transport. In 1958 the company merged with Reo Motor Car Company to form Diamond Reo, thus closing the independent stage of one of the most prestigious brands in the American trucking industry.