Answer: Meriwether Lewis
In 1803, the purchase of Louisiana aroused interest in the expansion of the territory of the United States to the west coast. Reason by which, after being annexed Louisiana, then President Thomas Jefferson, made arrangements for Congress to allocate money to make an expedition to the west territories.
In addition, Jefferson chose Lewis to lead the expedition, who, in turn, requested Clark's help. After which they crossed a great part of the North American territory until reaching the coast of the Pacific Ocean.