Saint Athanasius of Alexandria was a prominent Christian theologian and bishop in the 4th century. He is best known for his strong defense of the doctrine of the Trinity against Arianism, a belief that denied the divinity of Jesus Christ. Athanasius played a crucial role in the formulation of the Nicene Creed during the First Council of Nicaea in 325 AD, which affirmed the belief in the co-essentiality of the Father and the Son. Athanasius served as the Bishop of Alexandria multiple times, facing exile and opposition due to his beliefs. He is recognized as a Doctor of the Church and is celebrated for his writings, including "On the Incarnation," which explores the nature of Christ and salvation. His legacy continues to influence Christian theology today.