Who did Lewis and Clark get the Louisiana Purchase from?

Thomas Jefferson, the President of the U.S., bought Louisiana from France in 1803. Because of the Spanish and Russian exploration of the West Coast, they knew that Louisiana was part of a continent, but Nobody knew how big it was. Therefore, Jefferson commissioned Meriwether Lewis and William Clark - who, from all reports, Disliked each other intensely - to embark on a "Voyage of Discovery" in order to find out just What the U.S. had bought. The resultant Lewis & Clark Expedition, 1803-1806, mapped and described the terrain, as well as the Native population. This Native population saved their lives on more than one occasion, and one of them, Sackajewea, served as guide and translator for most of the trip. Needless to say, the Expedition was a huge success; Everybody was overjoyed to find out how Big and Rich the new land was. Meriwhether Lewis and William Clark became the 19th Century equivalent of Rock Stars.