Lewis and Clark were American explorers who led an expedition from 1804 to 1806 to map the newly acquired western territory of the United States after the Louisiana Purchase. Their journey aimed to find a water route to the Pacific Ocean and to study the land, plants, and animals they encountered. The expedition, officially known as the Corps of Discovery, was commissioned by President Thomas Jefferson. It included a diverse group of men and the assistance of Sacagawea, a Shoshone woman who served as a guide and interpreter. Their successful journey greatly expanded knowledge of the American West.