Louis the Pious was a Frankish king who ruled from 814 to 840 AD. He was the son of Charlemagne and became the sole emperor of the Carolingian Empire after his father's death. Louis is known for his attempts to maintain and organize the vast empire, which included parts of modern-day France, Germany, and Italy. During his reign, Louis faced challenges such as internal conflicts and external threats. He is often remembered for his efforts to promote Christianity and reform the church. However, his reign was marked by divisions among his sons, which eventually led to the fragmentation of the empire after his death.