The first Holy Roman Emperor crowned in 800 AD was Charlemagne, also known as Charles the Great. His coronation by Pope Leo III on Christmas Day is often cited as a foundational moment for the Holy Roman Empire, symbolizing the fusion of Roman, Christian, and Germanic elements. Charlemagne expanded the empire to include much of Western Europe, promoting learning and culture through the Carolingian Renaissance. His reign is considered a significant milestone in European history, as it set the stage for the development of modern European nation-states.