Athanasius, often called Athanasius, Saint (circa 293-373), was a Christian theologian and bishop as well as a Doctor of the Church, who championed the cause of Christian theology (orthodoxy) in the 4th-century struggle against Arianism. Born in Alexandria, Egypt, Athanasius received a classical education before entering the famous theological school of his native city. He was ordained a deacon as a young man and served as secretary to the bishop of Alexandria. It was then that he began to take a prominent position in the great theological struggle that culminated in the Council of Nicaea in 325. At Nicaea, Athanasius opposed Arius, the Alexandrian priest who advanced the doctrine known as Arianism; his life is intimately connected with the progress of the Arian controversy, and he was by far the most formidable antagonist encountered by that heresy. Athanasius formulated the homoousian doctrine, according to which the Son of God is of the same essence, or substance, as the Father; Arius, on the other hand, maintained that the Son was of a different substance from that of the Father and was merely a creature, much more perfect that any other creature, who was used by God in subsequent works of creation. Athanasius became bishop of Alexandria around 328 A.D. During the Arian controversy, politics mingled with theology, and each side labored to win the favor of the Roman emperor Constantine the Great. The Arian Party was both influential and very active at the imperial court. Athanasius was exiled five times; more than one-third of his episcopate was spent away from his see. His fifth and final exile lasted only four months and ended in 364. He spent the rest of his life in quiet labor at his post in Alexandria.
What I wish to bring to your attention is that he, like many other, was educated at Alexandria where he came in contact with many theological ideas which conflicted with the Jewish belief; especially concerning the Messiah.