Who led the first expedition to explore the Louisiana Territory?

In 1803 President Thomas Jefferson guided a splendid piece of foreign diplomacy through the U.S. Senate: the purchase of Louisiana territory from France. After the Louisiana Purchase Treaty was made, Jefferson initiated an exploration of the newly purchased land and the territory beyond the "great rock mountains" in the West. He chose Meriwether Lewis to lead an expedition, who in turn solicited the help of William Clark. The Expedition of the Corps of Discovery shaped a crude route to the waters of the Pacific and marked an initial pathway for the new nation to spread westward from ocean to ocean.

Source: National Archives