Hercules Louis Dousman (August 4, 1800 - September 12, 1868) was a trader and real-estate investor who became the first millionaire in Wisconsin.

Dousman was born on Mackinac Island, Michigan, and was brought into the fur trade by his father Michael, a prominent Mackinac trader. In 1826, Hercules left Mackinac Island and moved to the frontier settlement of Prairie du Chien, Wisconsin, where he worked as the assistant, and later as the partner of Joseph Rolette, the local agent of the American Fur Company.

In Prairie du Chien, Dousman built up a good reputation with both the Native Americans he traded with and his superiors, John Jacob Astor and Ramsey Crooks in the east. He replaced Joseph Rolette as agent in Prairie du Chien, and in 1842 Rolette passed away. During that same year, the American Fur Company filed for bankruptcy. In order to save the company Dousman entered a into a joint venture with Pierre Chouteau and Henry Sibley and bought the company's Western Division. Now that Dousman was his own boss, his earnings quickly expanded. He invested most of his money in real estate in both Prairie du Chien and the growing city of Milwaukee.

As his investments paid off, Dousman began to build up his 25 acre (101,000 m²) estate on an island in the Mississippi River at Prairie du Chien. In 1843, he built the famed House on the Mound, and in 1844 he married Jane Fisher, the wife of his former partner, Joseph Rolette. Together they had one son, Hercules Louis Dousman II, who was born on April 3, 1848. Less than two months later, Wisconsin became a state.

As Wisconsin became more and more civilized the fur trade industry fell apart, and Dousman was forced to find new ways to bring in money. Aside from his investments in real-estate, grain, and lumber, Dousman was a principal investor in Wisconsin's first Railroad, the Milwaukee & Waukesha, which later became known as the Milwaukee Road. Dousman was very influential in bringing the railroad to Prairie du Chien in 1857, which caused a small boom in the city's population. As Dousman owned much of the land in the city, he made a large profit from the population increase, and his net worth grew to over one million dollars, a sum that less than one-thousand Americans could claim to possess at the time.

Dousman died on September 12, 1868, as one of Wisconsin's most influential men. He is immortalized by the Villa Louis historic site in Prairie du Chien and as the central character of two novels by August Derleth. Dousman is buried at Calvary Cemetery in Prairie du Chien.