Patriarch Michael I Cerularius was the head of the Eastern Orthodox Church in Constantinople from 1043 to 1059. He is best known for his role in the events leading up to the Great Schism of 1054, which divided Christianity into the Roman Catholic and Eastern Orthodox Churches. His tenure was marked by conflicts with the Pope and the Western Church, particularly over issues of authority and theological differences. Cerularius was a strong advocate for the independence of the Eastern Church and opposed the Latin practices introduced by the Papal authority. His actions, including the excommunication of a papal legate, contributed to the growing rift between the two branches of Christianity, solidifying the schism that has persisted to this day.