Lewis and Clark, led by Meriwether Lewis and William Clark, are known for their exploration across North America from 1804 to 1806. Commissioned by President Thomas Jefferson, their expedition aimed to explore the Louisiana Purchase and find a Northwest Passage to the Pacific Ocean. Along their journey, they mapped vast territories, documented numerous plant and animal species, and established relationships with Native American tribes. Their expedition significantly contributed to the understanding of the American West and provided valuable information that encouraged westward expansion.