1774-1809. US explorer. He was commissioned
by president Thomas Jefferson to find a land
route to the Pacific with William Clark
(1770-1838). They followed the Missouri River
to its source, crossed the Rocky Mountains
(aided by an Indian girl, Sacajawea) and
followed the Columbia River to the Pacific,
then returned overland to St Louis 1804-06.
Formerly private secretary to President
Jefferson, he was rewarded for his expedition
with the governorship of the Louisiana
Territory. His death, near Nashville,
Tennessee, has been ascribed to suicide, but
was more probably murder. The detailed
journals kept of the expedition added to an
understanding of the region and facilitated
westward expansion.