Soldier and explorer (1770–1838) who, with Meriwether Lewis, undertook a two-year expedition in 1804 to discover a navigable route to the Pacific Ocean, in the process exploring and later describing much of the course along the Missouri River. Manuscript DS, signed “Wm. Clark, U.S. Agt. for Ind[ian] Af[fiar]s,” one page both sides, 7.5 x 12.25, August 17, 1810. An “Invoice of Sundry Packages, to be delivered by George Ingels, Esqr. to Wm. Linnard Esqr… by way of Pittsburg to Genl. Clark at St. Louis,” including such items as blankets, flints, “pocket cooking cases,” handkerchiefs, “guns or fowling pieces,” powder, “scalping knives,” tobacco, and more. Clark had been appointed a brigadier general (with the attendant duty as agent for Indian affairs) in 1807. During the War of 1812, he led several campaigns, and was perhaps uniquely qualified for an 1814 campaign along the Mississippi River, establishing a fort in present-day Wisconsin. A hint of mild wrinkling, a few small spots, and subtle show-through behind signature, otherwise fine, clean condition. Auction LOA John Reznikoff/PSA/DNA and R&R COA.