Sacagawea
While Sacagawea has been thought of as a guide for the expedition, she probably only gave directions a few times.  Her work as an interpreter certainly helped the party to talk with the Shoshone.  However, the most important thing she did for the group may have been being there during the hard journey, which showed they did not want to attack any Native Americans they came across.  While traveling through what is now Franklin County, Washington, Clark noted, "The Indian woman confirmed those people of our friendly intentions, as no woman ever accompanies a war party of Indians in this quarter," and, "the wife of Shabono our interpreter we find reconciles all the Indians, as to our friendly intentions a woman with a party of men is a token of peace."