Teodoro de Celles was a 12th-century canon and crusader who established the Order of the Holy Cross. Born around 1166, he originally served as a canon at the cathedral chapter in Liège. Seeking a more disciplined community life and a way to serve the faithful, he left the chapter with four other members. In 1211, he founded the mother monastery of his new religious community at Clair-Lieu, located near Huy.