Saint Hilaire of Poitiers was a prominent Christian bishop and theologian in the 4th century. Born around 315 AD in Poitiers, France, he became known for his strong defense of the Christian faith against Arianism, a belief that denied the divinity of Christ. His writings, particularly the "On the Trinity," contributed significantly to early Christian theology. Hilaire was appointed bishop of Poitiers and played a crucial role in the development of the early Church. He was later exiled for his beliefs but continued to write and preach. He is recognized as a Doctor of the Church and is celebrated on January 13, his feast day in the Roman Catholic Church.