Thomas Jefferson was born in a log cabin in 1743. His father, Peter Jefferson, was a prosperous Virginia planter. His mother, Jane Randolph Jefferson, was a member of the old and distinguished Randolph family of Virginia. In 1772, Thomas married Martha Wayles Skelton, a 24-year old widow. Patty, as Jefferson called her, shared her husband's love of music and played the harpsichord and piano. The marriage was a happy one despite Mrs. Jefferson's ill health. Of their six children, only two, both girls, lived to maturity. Martha Jefferson died in 1782. The death of his wife had a profound effect on Jefferson and probably influenced his return to politics, which he had previously considered abandoning.

In January of 1803, half a year before the Louisiana Purchase, Jefferson proposed the idea of an exploration expedition to Congress. In order to conceal its expansionist aims from England, France, and Spain, he suggested that the journey be presented as a "literary pursuit". Congress gave it's approval. Jefferson then chose his secretary, Meriwether Lewis to lead the expedition. Lewis selected William Clark, a frontiersman, as his co-leader. Jefferson instructed them to observe and note the physical features, topography, soil, climate, and wildlife of the land as well as the language and customs of its inhabitants. In 1806, Lewis and Clark returned with their valuable journals. They had successfully breached the mountain barrier of the West, built a fort on the Pacific Ocean at the mouth of the Columbia River while mapping and exploring much of the Northwest.

William Clark was born in Caroline County, Virginia. In 1784, the Clark family moved to Kentucky frontier and established a plantation called Mulberry Hill near present-day Louisville. As well as being a notable American explorer, he served as an army officer (1792-1796), during which time he participated in a number of engagements with Native Americans.

In 1803, he was chosen by his friend Meriwether Lewis to accompany the overland expedition to the Pacific. His observations of nature enlarged the findings of the expedition, while his journals and maps recorded its history. In 1807, after the expedition had returned, Clark was appointed superintendent of Indian affairs with headquarters at St. Louis. From 1813 to 1821, he served as governor of Missouri Territory. During the War of 1812, he led an expedition (1814) against the British and Native Americans in the upper Mississippi Valley. Upon reaching Prairie Du Chien, WI, he built fort Shelby. Later, with Auguste Chateau, he negotiated a number of important treaties with Native Americans and aided in suppressing the Winnebago and Black Hawk uprisings. He again served as superintendent of Indian affairs form 1821 till his death.

Meriwether Lewis was born in Albemarle County, outside Charlottesville, Virginia. He grew up in Virginia and Georgia as part of the Southern planter aristocracy. During his education, Lewis showed a special talent for history, which encompassed the fields of botany and zoology. Lewis also proved to be a keen observer of the natural world, an attribute he later put to good use during the Lewis and Clark expedition.

As well as being a notable American explorer, he was a captain in the army and served in a number of campaigns against the Native Americans before becoming secretary (1801) to friend President Jefferson. When selected to head the expedition for a land route to the Pacific Ocean, he chose William Clark as his associate. Lewis's fame rests upon that successful venture. In 1807, he was made governor of Louisiana Territory, with headquarters at St. Louis. In 1809, while traveling to Washington to prepare the journals of the expedition for publication, he died suddenly. While staying in a lonely inn on the Natchez Trace, he either committed suicide or was murdered, a subject still under controversy today.

Sacagawea was a Native American from the Shoshone tribe who served as an interpreter and guide for the Lewis and Clark expedition in 1805 and 1806. She was captured by members of the Hidatsa tribe and was sold as a slave to Missouri River Mandans. She was then sold to a Canadian trapper named Toussaint Charbonneau. She became one of his wives and gave birth to a son, Jean Baptiste, in February 1805. Explorers Meriwether Lewis and William Clark, who had spent the winter of 1804 and 1805 with the Mandans, hired Charbonneau as an interpreter and guide for the rest of the trip west. Sacagawea and her young son were allowed to go with the expedition when it set out in April 1805. When the expedition encountered a tribe of Shoshone led by her brother, Sacagawea obtained food, horses and more guides. This enabled the explorers to continue. Sacagawea, carrying her young son on her back, was legendary for her perseverance and resourcefulness. She and Charbonneau remained in North Dakota when the expedition returned to Missouri in 1806.

Scholars are not sure when Sacagawea died. One of the two Native American wives of Charbonneau died in 1812 and was thought to be Sacagawea. However, an old Native American woman who died on a reservation in 1884 also claimed to be Sacagawea and displayed considerable knowledge of the Lewis and Clark expedition. Of the many memorials to Sacagawea, the most famous is a statue in Washington Park in Portland, Oregon. In 2000, the United States Mint issued a new golden dollar coin with the image of Sacagawea on it. The coin depicts Sacagawea with her infant son asleep on her back.