Thor was an American manufacturer of motorcycles and motorcycle parts especially engines, founded in 1901 in Aurora, Illinois. From 1901 to about 1907 it made engines under license for Indian Motocycles (note spelling) of Springfield, Massachusetts, , which Thor was also allowed to sell on the open market. Thor also sold a large variety of parts especially cylinder heads. and when the agreement finally ended, entered the motorcycle market on its own selling complete bikes until about 1920. Some of its success were supplying engines to many motorcycle manufactures of the period, some record setting bikes in the early 1910s, and V-Twin engine with automatic valves.