Patrick Gass was one of the early enlistees in the expeditionary force led by Captains Meriwether Lewis and William Clark to survey the Missouri and Columbia Rivers in 1804-1806. In addition to his participation in the great journey, Gass was the author of the first published account of the expedition.

Gass's journal, which covered events from May 1804 to September 1806, was one of four kept by expedition members other than Lewis and Clark. In a published exchange of letters, Meriwether Lewis warned printer David McKeehan not to publish an unauthorized account of the expedition, but McKeehan publicly rebuked the threat and brought the Gass journal out in July 1807. By 1814, when Nicholas Biddle published the first official account of the expedition, the Gass journal was in its seventh edition, some with engravings depicting expeditionary events.

Gass was born in southern Pennsylvania on June 12, 1771, and was serving in the U.S. Infantry in Kaskaskia, Illinois, when Clark enlisted him for the expedition, perhaps in part because of his carpentry skills. In his journal, Gass describes events with clarity and often includes opinions about individuals and situations that are not recorded by Lewis and Clark. Some scholars are careful about his account, because the original journal was lost or destroyed and Gass had considerable help from McKeehan in completing the published work.

After he returned with the expedition to St. Louis in 1806, Sergeant Gass continued in the U.S. Army and was posted during the War of 1812, leaving the armed forces in 1815 with a disability. He married in 1831, at age sixty, to twenty-year-old Maria Hamilton. They had six children. Gass died on April 2, 1870, at age ninety-nine.