Christian feast day: Pope Gregory I (Eastern Orthodox Church, Eastern Catholic Church, and Anglican Communion)

Pope Gregory I, commonly known as Saint Gregory the Great, was the 64th Bishop of Rome from 3 September 590 until his death on 12 March 604. He is known for instituting the first recorded large-scale mission from Rome, the Gregorian mission, to convert the then largely pagan Anglo-Saxons to Christianity. Gregory is also well known for his writings, which were more prolific than those of any of his predecessors as pope. The epithet Saint Gregory the Dialogist has been attached to him in Eastern Christianity because of his Dialogues. English translations of Eastern texts sometimes list him as Gregory "Dialogos" from the Greek διάλογος, or the Anglo-Latinate equivalent "Dialogus". He is the second of the three Popes listed in the Annuario Pontificio with the title "the Great", alongside Popes Leo I and Nicholas I.

The Eastern Orthodox Church, officially the Orthodox Catholic Church, and also called the Greek Orthodox Church or simply the Orthodox Church, is one of the three major doctrinal and jurisdictional groups of Christianity, with approximately 230 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops via local synods. The church has no central doctrinal or governmental authority analogous to the pope of the Catholic Church. Nevertheless, the Ecumenical Patriarch of Constantinople is recognised by them as primus inter pares, a title held by the patriarch of Rome prior to 1054. As one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe. Since 2018, there has been an ongoing schism between Constantinople and Moscow, with the two not in full communion with each other.

The Eastern Catholic Churches or Oriental Catholic Churches, also known as the Eastern-Rite Catholic Churches, Eastern Rite Catholicism, or simply the Eastern Churches, are 23 Eastern Christian autonomous particular churches of the Catholic Church in full communion with the pope in Rome. Although they are distinct theologically, liturgically, and historically from the Latin Church, they are all in full communion with it and with each other. Eastern Catholics are a minority within the Catholic Church; of the 1.3 billion Catholics in communion with the pope, approximately 18 million are members of the eastern churches. The largest numbers of Eastern Catholics are found in Eastern Europe, Eastern Africa, the Middle East, and India. As of 2022, the Syro-Malabar Church is the largest Eastern Catholic Church, followed by the Ukrainian Greek Catholic Church.