According to the companion web site for the PBS series The West, "The official leader of the epic Lewis and Clark Expedition, Meriwether Lewis has been called 'undoubtedly the greatest pathfinder this country has ever known.' Lewis was born to a Virginia planter family in 1774. His father, who had been an officer in the American Revolution, died when Lewis was five years old...
"After briefly assuming the management of his family's Virginia plantation, Lewis joined the state militia in 1794 to help put down the Whiskey Rebellion in Pennsylvania. He continued his military career as an officer in the regular army, serving on the frontier in Ohio and Tennessee, and rising to the rank of captain by 1801, when he accepted an invitation from President Thomas Jefferson, an old family friend, to serve as his private secretary.
"Jefferson seems to have selected Lewis for this post with a view to placing him in charge of an already-contemplated transcontinental expedition. When Jefferson had proposed such an expedition in 1792, Lewis had been among the first volunteers, although his youth and inexperience disqualified him at the time. Now, with his frontier experience, Lewis made a perfect candidate in Jefferson's eyes, and the President soon set out a course of study that would equip him with the scientific skills needed for his journey. Between 1801 and the appropriation of funds for the expedition in 1803, Lewis studied with members of the faculty at the University of Pennsylvania and gathered information about his proposed route..."
The expedition, even in these days of dodgy education when it comes to history, is well known to American schoolchildren. Lewis' uncertain end is not so well known. PBS continues: "In September 1809 [Madison was president by then], Lewis set out for the nation's capital to answer complaints about his actions as governor [of the Missouri Territory], and on this trip died a violent but mysterious death in a tavern about 70 miles southwest of Nashville, Tennessee. Whether he committed suicide, as Jefferson believed, or was murdered, as his family maintained, remains uncertain even today."