“The Black Dwarf” is what his enemies called him. Athanasius was a dark-skinned Egyptian bishop who had few friends and plenty of enemies. He was exiled from the church five times by four Roman emperors, spending almost half of his 45 years as bishop of Alexandria in exile.
The reason for Athanasius’ exile-upon-exile was his persistence in declaring Arianism, the church’s most cherished theological thought of the day, as a heresy.
Arianism defined
Arianism is named after a priest from Libya who, when describing the doctrine of the Trinity, falsely claimed that “if the Father begat the Son, then he who was begotten had a beginning in existence, and from this it follows there was a time when the Son was not.” Regardless of its inconsistencies with the fullness of Scripture, this theological thought spread like wildfire throughout the land. In fact, many Christians were heard singing a tune that echoed Arius’ view: “There was a time when the Son was not.” Even today, there are few in the church who repeat Arius’ views despite the fact that Jesus Himself said He was God (John 10:30, John 17:11, etc.).
During the spread of this false doctrine, Athanasius was serving Jesus and His church as the chief deacon assistant to Bishop Alexander of Alexandria. These two men contended against Arius, exposing that his views denied the Trinity. Opposing Arius’ notion that Christ had an origin and came out of the Father, Alexander and Athanasius argued that Christ and the Father have always been eternally united as one in the Godhead (Colossians 1:16, Hebrews 1:1-2, etc.).
The Trinity: an essential doctrine
Athanasius contended that the doctrine of the Trinity was no minor, non-essential matter. Only one who was both fully human and fully God could atone for our our sin and depravity and hold the power to save us. The Christian understanding of salvation was at hand. Athanasius famously argued, “Those who maintain that there was a time when the Son was not rob God of His Word, like plunderers.”
Council of Nicea
The opposing thoughts caused so much controversy that the newly converted Emperor Constantine the Great 
intervened in 325 A.D. to call the Council of Nicea. He was cited as saying, “Division in the church is worse than war.” The council, comprised of around 300 bishops, drafted the first copy of the Nicene Creed. Athanasius had grown to be the most prolific writer on Nicene orthodoxy and orthodox Trinitarian doctrine. He saw major flaws in Arius’ writings and called his heresy the “forerunner of the Antichrist” (Athanasius, Orations Ar. 1:1).
The council ultimately condemned Arius as a heretic, exiled him from the church, and considered it illegal to possess his writings. Finally, peace was restored in the church and orthodox Christian beliefs were unified. Athanasius was hailed as a “noble champion for Christ.”
But this didn’t last long.
Athanasius exiled
Within months, Arius’ supporters convinced Emperor Constantine into ending Arius’ exile. When Athanasius conversely defended the doctrine of the Trinity and refused to recognize Arius and his writings back into God’s church, Arius and others began to spread false charges against him, including sorcery and treason. This accusation of treason forced Constantine to exile Athanasius from the land.
When Constantine died a few years later, Athanasius was restored to his post in Alexandria. But by this time, Arianism had become the dominant position of the day. He was banished and exiled four more times over the next several years.
Every story has a happy ending
Okay, so not every story has a happy ending. But this one does. By the time he was in his 70s, elderly Athanasius was permanently restored to his position in the church at Alexandria. During his exile, Athanasius wrote many books, including a biography on St. Antony that is considered the most historically reliable to this day. God used this biography to help lead many unbelievers to belief in Christ including St. Augustine. It also put him back in favorable light with the church.
Among his writings, Athanasius wrote a list of what he believed were the 27 divinely-inspired books of the New Testament. By the grace of God, his list is the one that the church eventually adopted and agreed with. And as far as Arianism is concerned, its lack of biblical basis led to its own demise. And as God has always been faithful to do, the gospel truths of Scripture prevailed throughout the ages, including the doctrine of the Trinity, which Athanasius so faithfully defended for so many years.