Eustathius of Antioch was a 4th-century Christian theologian and bishop who served as the patriarch of Antioch. Born in Side, he held the position of bishop in Beroea around 320 before ascending to the see of Antioch near 325. He is historically recognized for his active opposition to Arianism and his significant influence on the development of the Nicene Creed. Despite his theological contributions, his career was marked by ecclesiastical conflict and eventual exile.