Leo I, also known as Leo the Great, was a prominent pope who served from 440 to 461 AD. He is best known for his role in defining the nature of Christ and the importance of the papacy in the early Christian Church. Leo's teachings helped to solidify the doctrine of the Council of Chalcedon, which affirmed that Christ is both fully divine and fully human. During his papacy, Leo I also worked to strengthen the authority of the Roman Catholic Church and was involved in various diplomatic efforts. He famously confronted the Huns led by Attila, persuading them not to attack Rome in 452 AD. Leo's leadership and theological contributions have made him a significant figure in Christian history.