DOMINIC (1170–1221), Christian saint and founder of the Order of Friars Preachers, popularly known as the Dominicans. Born at Caleruega in Old Castile, Spain, of parents of the lesser nobility, Domingo de Guzmán received his early education for the clerical state from his archpriest uncle before going to Palencia to study arts and theology from 1186 until 1196. In the latter year he became a canon regular of the reformed cathedral chapter of his home diocese of Osma, where he was ordained to the priesthood and spent the next seven years. A diplomatic mission to Denmark in 1203 brought Dominic, as the traveling companion of his bishop, Diego d'Acebes, into contact with the Albigensian, or Catharist, movement in Languedoc.

This dualist heresy, which had its origin in the teachings of the Persian religious thinker Mani (216–276), had come to western Europe from the Bogomils of Bulgaria, spreading along medieval trade routes in...