Gregory the Great (540-604)

Pope Gregory I was the right man in the right place at the right time. Previously a government official who had sold all of his property in order to become a Benedictine monk, he was elected pope after the death of Pelagius II. Pelagious had gone to great effort to deal with problems like plague, hunger, floods, and advancing Lombard armies.
Already an able administrator, Gregory went right to work - one of his most important achievements was to break the power of the Lombards and thereby putting much of Italy under direct papal rule. The lands now controlled by the church became known as the Patrimony of Saint Peter. With these lands providing revenue and power, the office of the pope became the most powerful position in Italy - and one of the most powerful in Europe.
Religiously, Gregory increased his control over other bishops. A particular aspect of this was his expansion of the power of religious orders. He was also a strong advocate for the doctrine of celibacy for priests - something which was not commonly accepted at the time, but his efforts helped spread it more widely and gave it the imprimatur of being authoritative.
Other accomplishments of his included important aspects of the liturgy - for example, he is thought responsible for arranging the "Gregorian" chants which became central pieces of music in religious services.