St. Hilary of Poitiers was a Bishop and theologian called “Athanasius of the West.” Hilary of Poitiers is also one of the Doctors of the Church.

Hilary was raised as a pagan, receiving an education centered around Neoplatonism. He converted to Christianity and was elected bishop of Limonum (modern Poitiers) around 353. A short time later he emerged as the main defender of orthodoxy in the West against the Arians. He was condemned for his stand by the Council of Biterrae in 356 and exiled to Phrygia for four years by Emperor Constantius II. In 359, he regained prominence when he eloquently spoke out on his behalf at the Council of Seleucia. Hilary returned to Poitiers the following year.

In 361, Hilary had Arian Bishop Saturninus, who had been responsible for his exile, deposed. Constantius died in the same year, ending the Arian domination. Hilary also publicly disputed Auxentius, a major Arian, and defeated him.

His oratorical skills were matched by his lasting contributions to the faith through his writings. Aside from his commentaries on the Old and New Testaments, particularly the Psalms, his chief works were De Trinitate and De Synodis. Hilary died in Poitiers around 368.

A Doctor of the Church are certain men and women who are revered by the Church for the special value of their writings and preaching and the sanctity of their lives. They each made important and lasting contributions to the faith and are to be recognized for their great merits.

To be declared a Doctor of the Church, you have to meet three basic requirements:

1. First, you must have lived a life of exemplary holiness, or insignis vitae sanctitas (outstanding sanctity). In short, you have to be a saint.
   

2. Second, to be a Doctor of the Church you must have deepened the whole Church's understanding of the Catholic Faith with emins doctrina (eminent teaching). Which is to say, sanctity isn't enough. There are thousands of saints, but only 37 Doctors of the Church. To be a Doctor one must do more than just live the Faith. Rather, one must significantly and profoundly contribute to our understanding of Divine Revelation, helping us to know more deeply some truth about God and His actions in the World.
   

3. And third, a pope must officially declare you a Doctor. That being said, as the Church understands it, when a pope declares someone a Doctor of the Church, he's not so much making someone a Doctor as he is recognizing what the Holy Spirit has already done - that He has conferred the charism of Doctor upon them.