Final answer:
William Clark co-led the 1804 expedition, known as the Corps of Discovery, with Meriwether Lewis to explore the Pacific Northwest by the request of President Thomas Jefferson.
A) Lewis
Step-by-step explanation:
The individual who co-led an 1804 expedition to explore the Pacific Northwest was William Clark. The expedition, known as the Corps of Discovery, was tasked with exploring and mapping the territory acquired in the Louisiana Purchase. President Thomas Jefferson appointed Meriwether Lewis to head this expedition, and Lewis in turn selected William Clark as his co-leader. They set out to find the elusive Northwest Passage, gather geographic and scientific information, and establish American claims to the territory. Although they did not find the Northwest Passage, they brought back valuable information about the region's geography, biodiversity, and the indigenous peoples they encountered.
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