What Native American woman served as a guide on the Lewis and Clark expedition?

Sacagawea.

In 1803 Meriwether Lewis and William Clark were given a mandate by President Thomas Jefferson to find a route west to the Pacific Ocean. In preparation for their expedition, Lewis and Clark moved into Fort Mandan. They soon hired Charbonneau as an interpreter for their expedition and as a bonus, Charbonneau's Shoshone/Hidatsa wife, Sacagawea, would accompany the expedition west.

On February 11, 1805, shortly before the expedition was to set out, Sacagawea gave birth to her first child, a son. He was named Jean Baptiste Charbonneau and though not quite two months old at the onset of the expedition, the baby accompanied the group the entire way to the Pacific and back.

While Sacagawea became known as the Corps of Discovery's guide in many history books, in actuality she was part interpreter, part peacekeeper, and part horse trader. Since Sacagawea knew both the Shoshone and Hidatsa languages, she translated the Shoshone into Hidatsa by speaking to her husband. He in turn translated the Hidatsa into French for the rest of the expedition.