Hilarius or Saint Hilary (ca. 300 – 368) was bishop of Poitiers ('Pictavium') and considered an eminent doctor of the Western Christian Church. He was sometimes referred to as the malleus Arianorum ("hammer against Arianism") and the "Athanasius of the West". His name comes from the Greek word for happy or cheerful, the root also of the English word "hilarious". He died on January 13, which accordingly is his feast day in the Roman Catholic calendar of saints. In the past, when this date was occupied by the Octave Day of the Epiphany, his feast day was moved to 14 January.
So great was the respect in which he was held by the citizens of Poitiers that about 353, although still a married man, he was unanimously elected bishop (clerical celibacy was not required by the church until the late Middle Ages). At that time Arianism was threatening to overrun the Western Church; to repel the disruption was the great task which Hilary undertook. One of his first steps was to secure the excommunication, by those of the Gallican hierarchy who still remained orthodox, of Saturninus, the Arian bishop of Arles and of Ursacius and Valens, two of his prominent supporters.
About the same time, he wrote to Emperor Constantius II a remonstrance against the persecutions by which the Arians had sought to crush their opponents (Ad Constantium Augustum liber primus, of which the most probable date is 355). His efforts were not at first successful, for at the synod of Biterrae (Béziers), summoned in 356 by Constantius with the professed purpose of settling the longstanding disputes, Hilary was, by an imperial rescript, banished with Rhodanus of Toulouse to Phrygia, where he spent nearly four years in exile.
In 359 Hilary attended the convocation of bishops at Seleucia Isauria, where, with the Egyptian Athanasians, he joined the Homoousian majority against the Arianizing party headed by Acacius of Caesarea; from there he went to Constantinople, and, in a petition (Ad Constantium Augustum liber secundus), personally presented to the emperor in 360, repudiated the calumnies of his enemies and sought to vindicate his trinitarian principles.
His urgent and repeated request for a public discussion with his opponents, especially with Ursacius and Valens, proved at last so inconvenient that he was sent back to his diocese, which he appears to have reached about 361, within a very short time of the accession of Julian.
In 365 he published the Contra Arianos vel Auxentium Mediolanensem liber, in connection with the controversy; and also (but perhaps at a somewhat earlier date) the Contra Constantium Augustum liber, in which he pronounced that lately-deceased emperor to have been the Antichrist, a rebel against God, "a tyrant whose sole object had been to make a gift to the devil of that world for which Christ had suffered."
Hilary is sometimes regarded as the first Latin Christian hymnwriter, but none of the compositions assigned to him is indisputable.
The later years of his life were spent in comparative quiet, devoted in part to the preparation of his expositions of the Psalms (Tractatus super Psalmos), for which he was largely indebted to Origen; of his Commentarius in Evangelium Matthaei, an allegorical exegesis of the first Gospel; and of his no longer extant translation of Origen's commentary on Job.
He died in 368; no more exact date is trustworthy.
Editions of his writings were produced by Erasmus (Basel, 1523, 1526, 1528). An English translation by E. W. Watson appears in Nicene and Post-Nicene Fathers. Several of his works have appeared in Sources Chrétiennes (i.e. commentaries on Psalm 118 and St. Matthew, his attack on the emperor Constantius, on the Mysteries and most recently, in three volumes, on the Trinity).
Recent research has distinguished between Hilary's thought before his period of exile in Phrygia under Constantius and the quality of his later major works.
A vita of Hilary was written by Venantius Fortunatus c.550 but is not considered reliable. More trustworthy are the notices in Jerome (De vir. illus. 100), Sulpicius Severus (Chron. ii. 39-45) and in Hilary's own writings.
In the context of English educational and legal institutions Saint Hilary's festival lies at the start of the Hilary Term which begins in January.