When President Thomas Jefferson began drafting a proposal to explore the Louisiana Territory, Meriwether Lewis, his personal secretary, was the president’s obvious choice to command the expedition. After all, he had been working as Jefferson’s secretary since 1801 and was familiar with Jefferson’s fascination with the West and all the scientific and commercial opportunities it might contain. He was young, healthy and skilled in the ways of the frontier as well as being responsible and trustworthy in his secretarial duties.

Lewis was bright and articulate. He possessed a curious mind. Lewis noticed the world around him and was fascinated by it. He had a natural scientific outlook, which impressed the enlightened president.

Jefferson described him as “brave, prudent, habituated to the woods, & familiar with Indian manners and character.” Strong words for such a young man. Lewis was only 28 years old when he was handed the reins to one of the most important missions in the history of the United States—the Corps of Discovery.

Though he had very little formal education, Lewis received instruction before the expedition on everything from preserving plant and animal specimens to navigating by way of the solar system to determining exact latitude and longitude.

He studied modern medicine under the United States’ premier physician, Dr. Benjamin Rush, who assembled a medical kit for Lewis to use in the field. The crude kit contained a variety of drugs and implements standard for the day, including tools for bloodletting; purgatives, which members of the crew called “Rush’s Thunderbolts"; and opiates to administer for pain.

Indeed, his brief medical training paid off during the expedition when he treated not only members of the Corps, but Indians encountered along the way. He even amputated a young Indian boy’s toes during the expedition’s winter stay with the Mandans.

Jefferson noticed in Lewis a tendency toward depression, and if his journal entries are any indication, he did struggle with bouts of depression throughout the trip. Lewis often made no journal entries for extended periods of time. Some 144 days during the journey went unmarked, and historians speculate it was because of his depression.

After the expedition, Jefferson appointed Lewis governor of the Louisiana Territory. While Lewis promised Jefferson he would transform his journals and other field notes into a complete report, he died on October 11, 1809, without even starting the project. By most accounts, Lewis committed suicide; however, some have suggested Lewis's death is actually an unsolved homicide. He was 33 years old.

Lewis's co-captain, William Clark, was also aware of his friend’s depression, and after learning of Lewis's death he penned a letter to his brother that read, “I fear O! I fear the waight of his mind has over come him.”