Folcuin was a Frankish cleric and abbot who served as the Bishop of Thérouanne starting in 816. Born around 800 to Hieronymus, a descendant of Charles Martel, he was confirmed in his episcopal role by Louis the Pious. Throughout his career, he remained a loyal figure to the emperor and actively participated in various ecclesiastical synods. He died in Esquelbecq in December 855 while conducting an official visit.