Final answer:
Thomas Jefferson was the president who initiated and authorized the Lewis and Clark Expedition to explore and map the Louisiana Territory following its acquisition.
Step-by-step explanation:
The president who created the expedition and charged it with exploring the newly acquired lands was Thomas Jefferson. In 1803, Jefferson appointed Meriwether Lewis to organize an expedition to venture into the Louisiana Territory, which was acquired by the United States through the Louisiana Purchase.
The Lewis and Clark Expedition, also known as the Corps of Discovery, was tasked with mapping the territory and finding commercial possibilities, including a potential all-water route from the Missouri River to the Pacific Coast. Their journey from 1804 to 1806 played a crucial role in expanding the United States' geographical knowledge and setting the stage for westward expansion.