Alexander Hales (also Halensis, Alensis, Halesius, Alesius; called Doctor Irrefragabilis and Theologorum Monarcha) was a scholastic theologian. He was born at Hales , Gloucestershire, England, and died in Paris on August 21, 1245. He was educated in the monastery at Hales, studied and lectured at Paris, acquired great fame as a teacher in theology, and entered the Franciscan order in 1222.

Alexander was the first to write a commentary on the Sentences of Peter Lombard, before him theologians had always commented upon the scriptures. His Summa universae theologiae (first printed at Venice, 1475) was undertaken at the request of Pope Innocent IV, and received his approbation. It was finished by Alexander's scholars after his death. It is an independent work giving a triple series of authorities-- those who say yes, those who say no, and then the reconciliation or judgment. The authorities are chosen not only from the Bible and the Fathers, but also among Greek, Latin, and Arabic poets and philosophers, and later theologians. It treats in its first part the doctrines of God and his attributes; in its second, those of Creation and sin; in its third, those of redemption and atonement; and, in its fourth and last, those of the sacraments. In recognition of his efforts, Alexander was given the title of "Doctor Irrefragabilis".

Among the doctrines which were specially developed and, so to speak, fixed by Alexander of Hales, are those of the thesaurus supererogationis perfectorum , and of the character indelibilis of baptism, confirmation, and ordination. That doctrine had been written about much earlier by Augustine of Hippo and was eventually defined a dogma by the Council of Trent.

John Gerson tells us “The doctrine of Alexander is of a wealth surpassing all expression. It is said that someone asked St. Thomas what was the best manner of studying theology; he replied that it was by attaching oneself to a Master. And to which Doctor? he was asked again. To Alexander of Hales, the Angelic Doctor replied." (Gerson, Opera omnia.Epistola Lugdunum missa cuidam fratri Minori, vol. 1, p. 554.)

Compare Hailes Abbey, Gloucestershire, founded in 1245/6.