Catholic Encyclopedia (1913)/Advocatus Diaboli
Advocatus Diaboli (Advocate of the Devil), a popular title given to one of the most important officers of the Sacred Congregation of Rites, established in 1587, by Sixtus V, to deal juridically with processes of beatification and canonization. His official title is Promoter of the Faith (Promotor Fidei). His duty requires him to prepare in writing all possible arguments, even at times seemingly slight, against the raising of any one to the honours of the altar. The interest and honour of the Church are concerned in preventing any one from receiving those honours whose death is not juridically proved to have been "precious in the sight of God" (see Beatification and Canonization). Prospero Lamertini, afterwards Pope Benedict XIV (1740–58), was the Promoter of the Faith for twenty years, and had every opportunity to study the workings of the Church in this most important function; he was, therefore, peculiarly qualified to compose his monumental work "On the Beatification and Canonization of Saints," which contains the complete vindication of the rights of the Church in this matter, and sets forth historically its extreme care of the use of this right. No important act in the process of beatification or canonization is valid unless performed in the presence of the Promoter of the Faith formally recognized. His duty is to protest against the omission of the forms laid down, and to insist upon the consideration of any objection. The first formal mention of such an officer is found in the canonization of St. Lawrence Justinian under Leo X (1513–21). Urban VIII, in 1631, made his presence necessary, at least by deputy, for the validity of any act connected with the process of beatification or canonization.
Benedict XIV, De Beat. et Canon. Sanctorum, I, xviii.