He was born in Caleruega (Burgos) in 1170, in the bosom of a deeply believing and very distinguished family. His parents, Don Félix de Guzmán and Doña Juana de Aza, relatives of Castilian kings and kings of León, Aragón, Navarra and Portugal, descended from the founding counts of Castile. He had two brothers, Antonio and Manés.
From the age of seven to fourteen (1177-1184), under the tutelage of his uncle, Archpriest Gonzalo de Aza, he received a careful moral and cultural formation. During this time, spent mostly in Gumiel de Izán (Burgos), he awakened his vocation to the ecclesiastical state.
From the age of fourteen to twenty-eight (1184-1198), he lived in Palencia: six years studying Arts (higher Humanities and Philosophy); four, Theology; and another four as professor of the General Study of Palencia.
When he finished his Arts degree in 1190, and received the tonsure, he became a Regular Canon in the Cathedral of Osma. It was in the year 1191, already in Palencia, when in a heroic act of charity he sold his books to alleviate the poor of the famine that was ravaging Spain.
After completing his theology studies in 1194, he was ordained a priest and was appointed Regent of the Chair of Sacred Scripture in the Studium of Palencia.
At the end of his four years of teaching and university teaching, when he was twenty-eight years old, he joined his Chapter, where immediately, due to his outstanding intellectual and moral qualities, the Bishop entrusted him with the presidency of the community of canons and the government of the diocese as Vicar General of the diocese.
In 1205, by order of King Alfonso VIII of Castile, he accompanied the Bishop of Osma, Diego, as extraordinary ambassador to arrange the wedding of Prince Ferdinand at the Danish court. For this reason, he had to make new trips, always accompanying Bishop Diego to Denmark and Rome, deciding during them his destiny and clarifying definitively his already old missionary vocation. In his comings and goings through France, he learned of the ravages that the Albigensian heresy was wreaking on souls. In agreement with Pope Innocent III, in 1206, at the end of the embassies, he established himself in Langüedoc as a preacher of the truth among the Cathars. He refused the bishoprics of Conserans, Béziers and Comminges, to which he had been canonically elected to remedy the evils that religious ignorance produced in society. In 1215, he established in Toulouse the first house of his order of preachers, ceded to Dominic by Peter Sella, who with Thomas of Toulouse was associated with his work.
In September of the same year, he arrived again in Rome on a second trip, accompanied by the Bishop of Toulouse, Fulco, to attend the Lateran Council and request the Pope's approval of his Order as a religious organization of canons regular. On his return from Rome he chose with his companions the Rule of St. Augustine for his Order and in September 1216, he returned on a third trip to Rome, taking with him the Rule of St. Augustine and a first draft of Constitutions for his Order. On December 22, 1216 he received from Pope Honorius III the Bull "Religiosam Vitam" by which he confirmed the Order of Friars Preachers.
The following year he returned to France and in the month of August he dispersed his friars, sending four (4) to Spain and three (3) to Paris, deciding to go to Rome. There his thaumaturgic power was manifested with numerous miracles and the number of his friars increased in an extraordinary way. Months later he sent the first friars to Bologna.
At the end of 1218 Domingo came back to Spain where he visited Segovia, Madrid and Guadalajara.
By mandate of Pope Honorius III, on a fifth trip to Rome, he gathered in the convent of San Sisto the nuns dispersed in the various monasteries of Rome, to obtain for the Friars the convent and the Church of Santa Sabina.
On the Feast of Pentecost of 1220 he attended the first General Chapter of the Order, celebrated in Bologna. In it the second part of the Constitutions were written. A year later, in the following Chapter also celebrated in Bologna, they agreed on the creation of eight Provinces.
With his Order perfectly structured and more than sixty (60) communities in operation, physically exhausted after a brief illness, he died on August 6, 1221, at the age of fifty-one, in the convent of Bologna, where his remains are buried. In 1234, his great friend and admirer, Pope Gregory IX, canonized him.
