Pope St. Leo the Great (d. 461). This guy did it all. Elected to the papacy on August 11, in the year 440, Leo defended the role of the papacy as being one of universal pastor for the Church, as would befit the successor to Peter, the head of the Apostles. When the bishops of the Church met together at the Fourth Ecumenical Council (better known as the Council of Chalcedon) in 451, Leo's absence did not dilute his influence as "chief shepherd of the flock." He sent a statement to the participants of the Council which, when read aloud during the proceedings, caused the bishops gathered to declare: "This is the faith of the Fathers ... Peter has spoken thus through Leo..." This famous statement of faith, composed by the pope himself and now known as the "Tome of Leo" was endorsed by the Council. Leo served the Church as pope for over twenty-one years, making him one of the longest-serving popes in history. He is, perhaps, most famous for meeting the infamous Attila the Hun at the gates of Rome in 452 and persuading the feared ruler not to sack the Eternal City. Leo died in 461 and rests underneath this altar in a chapel dedicated to him in St. Peter's Basilica.
And speaking of St. Peter's, Leo is but one of many, many notable leaders of the Church who are buried within this architectural treasure. Leo is called "the Great" because he was a great leader for the Church -- arguably "the greatest." But he exercised this leadership but for one goal: unity. The office of the pope, the "first among equals" among the Church's bishops, is derived not from an idea but from a promise -- a promise of Christ. When asked why we insist on recognizing the successor to Peter as the leader of the Church, we can take solace in the fact that we do this not for any frivolous reason nor because of any man-made invention or innovation; we do so solely because Christ willed it to maintain the visible unity of his Church throughout the ages. Never forget the promise of our Lord in Matthew 16:18-19: "And I tell you," said Jesus to the disciple that he was about to re-name Peter, "you are Peter, and on this rock I will build my Church, and the gates of Hades shall not prevail against it. I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall by loosed in heaven." This entrustment of Jesus' pastoral care of the flock to Peter was later reiterated in the exchange between Jesus and Peter recorded in John 21:15-17. And if you'd like to read more about Peter's place in the New Testament, here is a great article on the subject.
The point is, Leo was the successor to Peter just as our current pope, Benedict, is the successor to Leo and, ultimately, to Peter. The papacy is a wonderful gift from Christ to his Church and, nearly 2,000 years later, it still bears fruit in allowing the constant, visible leadership of the Church in a world that is increasingly hostile to her message of love, reconciliation and salvation. And union with Peter's successor is a sure sign of that unity for which Christ fervently prayed (John 17:11). May we continue to seek this unity for all who follow Christ.
Pope St. Leo, pray for us!