Born at Poitiers, St. Hilary was a leading defender of the Church against the Arian heresy. He wrote twelve books about the Blessed Trinity as well as commentaries on St. Matthew’s Gospel and the Psalms.

“Grant, we pray, almighty God, that we may rightly understand and truthfully profess the divinity of your Son, which the Bishop Saint Hilary taught with such constancy.
Through our Lord Jesus Christ, your Son, who lives and reigns with you in the unity of the Holy Spirit, one God, for ever and ever.” (Collect)
~ from the Proper of Saints, Daily Roman Missal