Pope Celestine I served as the head of the Roman Catholic Church from 422 to 432 AD. He is known for his efforts to promote Christian doctrine and combat heresies during a time of theological conflict. His papacy was marked by the establishment of the Council of Ephesus in 431, which addressed issues related to the nature of Christ and the role of the Virgin Mary. Celestine I also focused on missionary work, sending bishops to various regions to spread Christianity. He is remembered for his commitment to the faith and his role in shaping early Christian teachings, contributing to the development of the Catholic Church.