Who is Pierre Dorion from The Journals of Lewis and Clark and what is their importance?

Pierre Dorion was a half-French, half-Teton trapper who had been living with the Teton Sioux for over a decade. Lewis hired Pierre as an interpreter. Dorion was instrumental in instigating the peace process between the Yankton Sioux and their neighboring tribes. Dorion is also charges with collecting and transporting various Indian chiefs to St. Louis and to Washington, as promised by the speeches of the captains. These visits will eventually prove extremely important for the President of the United States in building the relationships between the American government and the various Indian tribes.