DIETHER VON ISENBURG. — Archbishop of Mainz, b. 1412, d. 7 May 1482 at Aschaffenburg. Elected Archbishop of Mainz in 1459, he did not receive confirmation from Pius II. He thus became the driving force behind anti-Roman activity in Germany and promoted the convocation of a general council to renew the decrees of the Council of Basel. In 1462 he was compelled to renounce the archiepiscopal dignity in favor of Adolf of Nassau, who was confirmed by the Pope. Re-elected Archbishop in 1475, this time he received papal confirmation. In 1477 he founded the University of Mainz.
Bibl.: K. Menzel, D. von I., Erzbischof von Mainz, Erlangen 1868; A. Veit, D. von I., in LThK, III, cols. 317, with bibliography; H. Jedin, Geschichte des Konzils von Trient, Italian trans., Brescia 1949, pp. 45-46. Silvio Furlani