William Clark was a Virginian whose
older brother was Gen. George Rogers Clark. His friend, Meriwether Lewis,
was asked by President Jefferson to explore the Louisiana Territory and
wanted Clark's help. In 1804, they and a few other explorers set off on
their expedition. Along the way they met Sacajawea, an Indian woman, who
served as their guide. On November 15, 1805, they became the first people
to cross the continent. The trip took two years to journey across the continent
and back.