Diego de Acebo was bishop of Osma (Castile, Spain) from 1201 to 1207.

Accompanied by his canon

Canon (priest)

A canon is a priest or minister who is a member of certain bodies of the Christian clergy subject to an ecclesiastical rule ....

, the future Saint Dominic

Saint Dominic

Saint Dominic , also known as Dominic of Osma, often called Dominic de Guzmán and Domingo Félix de Guzmán was the founder of the Friars Preachers, popularly called the Dominicans or Order of Preachers , a Catholic religious order...

, he travelled ad Marchias Daciae (to Denmark

Denmark

Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

) in 1203 or 1204 to secure a bride for crown prince Ferdinand, son of Alfonso VIII of Castile

Alfonso VIII of Castile

Alfonso VIII , called the Noble or el de las Navas, was the King of Castile from 1158 to his death and King of Toledo. He is most remembered for his part in the Reconquista and the downfall of the Almohad Caliphate...

. They made a second journey in 1204 or 1205 intending to bring the girl back with them, but found that she had meanwhile died. They returned by way of Rome, where Diego unsuccessfully petitioned Pope Innocent III

Pope Innocent III

Pope Innocent III was Pope from 8 January 1198 until his death. His birth name was Lotario dei Conti di Segni, sometimes anglicised to Lothar of Segni....

 to be entrusted with a mission to the northern pagans. Instead, continuing their journey via Cîteaux, Diego and Dominic began the work of conversion of the Cathars. Diego was instrumental in the foundation of Prouille

Prouille

Prouille or Prouilhe , "cradle of the Dominicans", where the first Dominican house, a convent, was founded in late 1206 or early 1207, is a hamlet in Languedoc, France, lying between Fanjeaux and Bram , at the point where the road from Castelnaudary to Limoux crosses the road from Bram to...

 and took part in the early Cathar-Catholic debates at Verfeil, Pamiers

Pamiers

Pamiers is a commune in the Ariège department in the Midi-Pyrénées region in southwestern France. It is a sub-prefecture of the department. Although Pamiers is the largest city in Ariège, the capital is the smaller town of Foix...

 and Montréal

Montréal, Aude

Montréal is a commune just south of Carcassonne in the Aude department, a part of the ancient Languedoc province and the present-day Languedoc-Roussillon region in southern France.-Population:-References:*...

, but was soon afterwards ordered by the Pope to return to his diocese, where he died on 30 December 1207.