Elwood P. Haynes (October 14, 1857 – April 13, 1925) was an American inventor, metallurgist, automotive pioneer, entrepreneur and industrialist. He invented the metal alloys stellite and martensitic stainless steel and designed one of the earliest automobiles made in the United States. He is recognized for having created the earliest American design that was feasible for mass production and, with the Apperson brothers, he formed the first company in the United States to produce automobiles profitably. He made many advances in the automotive industry.

Early in his career, while serving as a superintendent at gas and oil companies during Indiana's gas boom, Haynes invented several devices important to the advance of the natural gas industry. When working for the Indiana Natural Gas and Oil Company, he oversaw the construction of the first long-distance natural gas pipeline in the United States, connecting Chicago with the Trenton Gas Field 150 miles (240 km) away. He began to formulate plans for a motorized vehicle in the early 1890s; he successfully road tested his first car, the Pioneer, on July 4, 1894—eight years after the first automobile was patented in Germany. He formed a partnership with Elmer and Edgar Apperson in 1896 to start Haynes-Apperson for the commercial production of automobiles, and he renamed it Haynes Automobile Company in 1905, following the loss of his partners.