GRETSER, JAKOB. - Jesuit theologian, b. at Markdorf (Baden) on 27 March 1562, d. at Ingolstadt on 28 Jan. 1625. Having entered the Society of Jesus at Landsberg, he studied at the University of Ingolstadt, where he later taught philosophy (1589–92) and then scholastic and moral theology, succeeding his master Gregorio di Valencia. In his controversies with the Protestants he faced Junius, Wittaker, Hunnius, Dresser, Pappus, Reinack, against whom he wrote many works, which give him an important place in the controversy.
His major work is the defence of Bellarmino: Controversiarum R. Bellarmini amplissima defenita (Ingolstadt 1607–1609). Another fundamental work is the De Cruce Christi (ibid. 1598–1605), a veritable mine of erudition. Also worthy of mention are: De iure et more prohibendi, expurgandi et abolenati libros haereticos et noxios (ibid. 1603), composed in support of the Index expurgatorius, caused to be published by Filippo II and printed at Antwerp in 1571, which had aroused the strongest resentment among Protestant writers; Dissertatio pro sacratissima Corporis Christi solemnitate et sacrosanctae Eucharistiae cultu (ibid. 1612).
G. left altogether 233 works on the most diverse questions, preserved in the sole edition edited by P. G. Kolb (17 vols., Ratisbon 1734–42).