The legendary king of the Franks known for uniting much of Western Europe was Charlemagne. Crowned as Emperor of the Romans in 800 AD, Charlemagne expanded his kingdom through military conquests and is credited with revitalizing learning and culture during the Carolingian Renaissance. His reign marked a significant transition towards feudalism in Europe and the establishment of the Holy Roman Empire. Charlemagne's legacy includes the promotion of Christianity and the preservation of classical heritage, which influenced subsequent European history.