Peter Nolasco was a young Languedocian merchant who fled to Catalonia after the Albigensian Crusade and entered the service of King James I of Aragon. Wealthy and pious, he devoted his wealth from his early thirties to ransoming Christian captives from the slave-markets of Valencia, Granada, and the Moorish coast.
On August 1, 1218, according to the unanimous tradition of his order, the Virgin Mary appeared simultaneously to him, to King James I, and to the canon Raymond of Penyafort (the great Dominican canon-lawyer), asking that a new order be founded for the redemption of captives. Ten days later, in Barcelona cathedral, before the king and the bishop, Peter Nolasco received the white habit and the four vows of the new Order of Our Lady of Mercy for the Ransom of Captives — the four vows being the usual three (poverty, chastity, obedience) plus a fourth, to give up their own freedom and lives in exchange for captives if necessary.
Through the 13th, 14th, and 15th centuries the Mercedarians ransomed tens of thousands of captives from North African slave-markets, alongside the parallel Trinitarian Order of John of Matha. Peter Nolasco himself led several of these expeditions across the western Mediterranean. He died at Barcelona on Christmas night 1256, at the prayer 'In manus tuas, Domine,' and was canonized in 1628.