Serapion of Algiers was a 13th-century Mercedarian priest and martyr who was born in London. A member of the Order of the Blessed Virgin Mary of Mercy, he is recognized as the first martyr of his religious order. His life was marked by various roles, including serving as a warrior monk and participating in military efforts during the Crusades and the Reconquista. He is remembered for his dedication to redeeming Christian captives from captivity in Muslim territories.