Pope Gregory I (c. 540 – 12 March 604), commonly known as Saint Gregory the Great, was the bishop of Rome from 3 September 590 to his death.  He is known for instigating the first recorded large-scale mission from Rome, the Gregorian Mission, to convert the then-pagan Anglo-Saxons in England to Christianity.  Gregory is also well known for his writings, which were more prolific than those of any of his predecessors as pope.  

During his papacy, he greatly surpassed with his administration the emperors in improving the welfare of the people of Rome, and he challenged the theological views of Patriarch Eutychius of Constantinople before the emperor Tiberius II. Gregory regained papal authority in Spain and France and sent missionaries to England, including Augustine of Canterbury and Paulinus of York. The realignment of barbarian allegiance to Rome from their Arian Christian alliances shaped medieval Europe. Gregory saw Franks, Lombards, and Visigoths align with Rome in religion. He also combated the Donatist heresy, popular particularly in North Africa at the time.

Throughout the Middle Ages, he was known as "the Father of Christian Worship" because of his exceptional efforts in revising the Roman worship of his day. His contributions to the development of the Divine Liturgy of the Presanctified Gifts, still in use in the Byzantine Rite, were so significant that he is generally recognized as its de facto author.

Gregory is one of the Latin Fathers and a Doctor of the Church. He is considered a saint in the Catholic Church, and the patron of musicians, singers, students, and teachers.

Source: https://en.wikipedia.org/wiki/Pope_Gregory_I

St. Gregory the Great - c. 591 A.D. Pastoral Rule St. Gregory the Great - c. 590 A.D. Registry of Letters St. Gregory the Great - c. 595 A.D. Morals on the Book of Job