Servus Servorum Dei
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Cyclopedia of Biblical, Theological and Ecclesiastical Literature [1]
(Servant of the servants of God), an official title of the Roman pontiffs, in use since the time of Gregory the Great, by whom, according to his biographer, Paul the Deacon, it was assumed as a practical rebuke of the ambitious assumption of the title of "OEcumenical (or universal) Patriarch" by John, surnamed Nestentes, or the Faster, contemporary patriarch of Constantinople. Other Christian bishops previous to Gregory had employed this form, but he was doubtless the first of the bishops of Rome to adopt it as a distinctive title. It is found in all the letters of Gregory preserved by the Venerable Bede in his history.