Theologian; b. Geldern, Rhineland, Nov. 8, 1864; d. Münster, Oct. 10, 1943. After his ordination in 1887 he spent some time in parish work. In 1889 he taught at the Münster theological seminary, and in 1898 was a lecturer at the University of Münster. In 1904 he was named professor, and until 1933 taught patrology, history of dogma, Church history, and dogmatic theology. Diekamp advanced the science of patrology and history of dogma by his editions of and commentaries on the Fathers. His works are distinguished by an extraordinary accuracy, thoroughness, and clarity. In 1902 he founded the Theologische Revue, and in 1923 he became editor of the Münsterische Beiträge zur Theologie. Of his numerous writings the following are especially important: Die Gotteslehre des hl. Gregor v. Nyssa (Münster 1896), Die origenistischen Streitigkeiten im 6. Jahrhundert u. das 5. allg. Konzil (Münster 1899), Doctrina Patrum de incarnatione Verbi (Münster 1907), Über den Ursprung des Trinitätsbekenntnisses (Münster 1911). His best-known work, representing the most important German effort in a Thomistic direction, is Katholische Dogmatik nach den Grundsätzen des hl. Thomas, 3 v. (Münster 1912–14); new edition by K. Jüssen (Münster 1958–62); Latin version by A. Hoffmann, Theologiae dogmaticae Manuale, 4 v. (Paris-Tournai-Rome 1932–34).
Bibliography: b. altaner, Historisches Jahrbuch des Görres-Gesellschaft 62–69 (1942–49) 916–919. m. schmaus, Neue deutsche Biographie (Berlin 1953–) 3:645.