Saint Gregory the Great is so called because he was truly a great leader starting as a Prefect of Rome before he was thirty. Afterwards, the church flourished under his wise and holy influence as a monk, deacon, priest, papal nuncio, and abbot. At fifty he was elected Pope by the clergy and the people of Rome.During his day during the sixth century the church was undergoing ferocious attacks by Huns, Goths, and Lombards with rampant strife that caused great hardships and tragedy. The population of Rome plumetted from a million to 15,000 due to invasions, pestilence, and diseases. Gregory's courage, leadership, action, and prayers, helped unite the church together.
No doctor of the church or member served in more offices or position than Gregory. He was the first Pope to be declared a doctor. He shares that distinction with St Leo, the only other pontiff to become a doctor, and he was born before Gregory.
Gregory was firm and direct in removing unworthy priests from office and was a great Benedictine reformer and strengthened the respect for doctrine.
http://catholicism.org/gregory-great.html
