Controversialist, born at Sackingen, Baden, Germany, in 1568; died at Munich, Bavaria, 23 February, 1631. After entering the Society of Jesus in 1589 and completing his studies, he taught the classics at Freiburg and was professor of philosophy and of moral and dogmatic theology at Ingolstadt. He was appointed rector of the college of Ratisbon in 1605, and of the college of Munich in 1607, which post he held until 1623. In 1628 he was reappointed to the rectorship of Munich, and was still holding the office when a stroke of apoplexy ended his life. Besides his literary and scholastic attainments (for he was regarded as a genius), he possessed uncommon executive ability, and in spite of his extreme humility was consulted not only by his religious superiors, but also by Maximilian I, Elector of Bavaria, who often sought his advice and entrusted to his care affairs of moment, which he discharged with much success.

His principal works are: "Tyrannicidium" (Munich, 1611) and "Catholisch Pabsttumb" (Munich, 1614). The former, which appeared both in German and Latin, was an answer to certain calumnies printed by a Calvinist with reference to the teaching of the Society of Jesus on the subject of Tyrannicide. Father Keller showed that the Jesuit teaching was no other than that of the greatest theologians, both Catholic and Protestant. The work on the papacy was a reply to aspersions cast on the Holy See by Jacob Heilbrunner, and is a veritable treasure-house of answers to the objections of Protestants. It was followed by a public debated between Keller and Heilbrunner, in which the latter was completely silenced. Keller published fourother works which were the last word on the subject, and left his adversary utterly defeated. Among his other works are: "Ludovicus IV Imperator defensus contra Bzovium" (Munster, 1618), a work of real historical value; "Vita R.P. Petri Canisii". Of local rather than general interest are a number of other polemical writings, e.g. "Litura seu castigatio Cancellariae Hispanicae a Ludovico Camerario, Excancellario Bohemico, Exconciliario Heidelbergensii . . . instructae"; "An der theil Anhaldischer Cancellay"; "Tubus Galilaeanus"; "Rhabarbarum domandae bili quam in apolgiae sua proritavit Ludov. Camerarius propinatum". He published a large number of other writings, sometimes under his own, sometimes under an assumed name, mostly controversial.

J. H. Fisher.