Peter M. Weiser (October 3, 1781 – death between 1813 and 1828) was an American soldier and member of the Corps of Discovery on the Lewis and Clark Expedition.
In the late spring of 1806, while the Corps was camped near present-day Kamiah in north central Idaho, he took part in a detached search expedition for food in the surrounding mountains.
In 1807 Corps of Discovery members John Potts and George Drouillard, joined the party of Spanish fur trapper Manuel Lisa on the Upper Missouri River.
Lisa and his company of 42 men (including John Baptiste Champlain and Benito Vázquez)[3] moved up the Missouri until they reached the mouth of the Yellowstone River.
After ascending the Yellowstone some 170 miles, they established Fort Raymond, a trading post at the mouth of the Bighorn River in present-day Montana.
Weiser and Potts were at Fort Raymond in early July 1808 and the two men contracted to enter into a joint venture,[4] signing a note for $450 for supplies to Lisa's company.
The new company decided to relocate its main location to the Three Forks of the Missouri, and the following spring of 1810, Weiser presumably accompanied Henry to build a fort there.