Pierre Chouteau (1789–1865) was a fur trader (beaver, deer, buffalo) and son of one of the founders of St. Louis, some 800+ miles down the Missouri from Pierre. The fort named after him was built in 1832, a strategic spot for John Jacob Astor's American Fur Company, located as it was halfway between the company's headquarters in St. Louis and its northernmost posts in North Dakota and Montana. The fort was in use for a quarter century and was visited by George Catlin and Audubon.
More interesting, perhaps, is the Verendrye plate, a lead plate buried in 1743 by Pierre de la Verendyre to claim the country for France, and discovered by schoolchildren in 1913. As far as I know, the state's heritage has nothing French in it beyond the name (with its anglicized pronunciation) of the capital and Bon Homme County, but no other of the state's 66 counties. All those French explorers and traders left little behind. It wasn't till the Scandinavians & Germans that the state was really settled by Europeans.