Pope Leo I (b. 430) lived from the years 440 to 461. An unrelenting foe to heresies, he was the first pope to have "the Great" attached to his name, and only the second of all time (the other is Pope Gregory I). Leo, whose name means Lion in Latin, did much for the Universal Church, and as such is considered one of 33 Doctors of the Church. This is a title which started in 1298, and Leo was promoted to this title in 1754.
Pope Leo, who was 30 years old when St. Augustine died in 430, did much for the Catholic Church. In fact, Pope Leo met Augustine while Leo was an acolyte, or someone training to be a priest. Pope Leo confronted and destroyed many heresies at the time, many of which were related to Christ's human and divine nature. At a council, he proclaimed his view that Christ was both man and God, and all those attending gave their accordance, saying that Leo was following Peter, the first Pope.
One of the most spectacular events to happen during Leo's papacy was his encounter with the ruthless Attila the Hun, known as the Scourge of God, whose goal was world domination. He warred against many nations around the world and conquered them wherever he went. His armies killed men, women, and children. In fact, Attila was famous for literally ripping apart his opponents.
Then he arrived in Italy. Italy was a very important country, because it was the seat of the Roman Empire. In fact, the Huns were the only real threat facing the Roman Empire, and was a gateway to the entire European continent. Taking Italy would be a disaster for the entire Western World. An interesting fact is that the history of Venice is intertwined with that of Attila the Hun. To escape the brutality of Attila, many Italians fled to the islands of Venice for protection. Eventually they built a great city there. Attila planned to destroy Italy, and conquered it, as he had done with many other places.
When he arrived in Rome, he met with the Pope. While there, Attila saw Sts. Peter and Paul appearing with swords standing near the Pope. Those around Attila were surprised that he decided not to attack Rome, so he explained to them what he had witnessed. Because of the Pope's eloquence in fending off Attila, he is known as the Shield of God.
Pope Leo I deserved his prototypical title of Great, as well as his namesake of Lion, for he defended the doctrines of the Church against heresy and attack, like a lion protects its young. With the help of God, Pope Leo the Great is known as one of the most faithful servants of Christ.