As he made arrangements for the Expedition, Lewis concluded it would be desirable to have a co-commander. With Jefferson's consent, he offered the assignment to his friend and former commanding officer, William Clark, who was living with his brother, George Rogers, at Clarksville, Indiana Territory. Clark accepted, stating in his reply, "The enterprise &c. is Such as I have long anticipate and am much pleased.... My friend, I do assure you that no man lives whith whome I would perfur to undertake Such a Trip &c. as yourself."
Also a native Virginian, Clark, born August 1, 1770, was 4 years older than Lewis. In capability and background, he and Lewis shared much in common. They were relatively young, intelligent, adventurous, resourceful, and courageous. Born leaders, experienced woodsmen-frontiersmen, and seasoned Army officers, they were cool in crisis and quick to make decisions. Clark, many times over, would prove to be the right choice as joint leader of the Expedition.
In temperament Lewis and Clark were opposites. Lewis was introverted, melancholic, and moody; Clark, extroverted, even-tempered and gregarious. The better educated and more refined Lewis, who possessed a philosophical, romantic and speculative mind, was at home with abstract ideas; Clark, of a pragmatic mold, was more of a practical man of action. Each supplied vital qualities which balanced their partnership.
Their relationship ranks high in the realm of notable human associations. It was a rare example of two men of noble heart and conscience sharing responsibilities for the conduct of a dangerous enterprise without ever losing each other's respect or loyalty. Despite frequent stress, hardships, and other conditions that could easily have bred jealousy, mistrust or contempt, they proved to be self-effacing brothers in command and leadership. During their long journey, there is not a single trace of a serious quarrel or dispute between them.
After the Expedition, Lewis was appointed Governor of the Louisiana Territory; Clark was promoted to Brigadier General and appointed to the Superintendency of Indian Affairs. Lewis, at age 35, died tragically on October 11, 1809, just three years after the Expedition. His grave lies within Natchez Trace National Parkway, near Hohenwald, Tennessee. Thomas Jefferson, who held life-long affection for his protege, is credited with the Latin inscription on Lewis' tombstone: Immaturus obi: sed tu felicior annos Vive meos, Bona Republica! Viva tuos. (I died young: but thou, O Good Republic, live out my years for me with better fortune.)
Clark lived a long and productive life in St. Louis, dying September 1 1838, at age 68. He is buried in the Clark family plot. In deserved tribute, both Meriwether Lewis and William Clark are recognized members of that generation of our young nation's heroes who launched within themselves a drive of nationalistic vision and patriotic will that would form the spirit and richness of American history itself.