Jacob Keller (1568 – 23 February 1631) was a German Jesuit theologian, author, and religious instructor.
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.
In 1628 he was reappointed to the rectorship of Munich, and was still holding the office when an apoplexy ended his life.
The former, which appeared both in German and Latin, was an answer to a Calvinist attack on the teaching of the Society of Jesus on the subject of tyrannicide in which Keller argued that the Jesuit teaching followed prominent theologians, both Catholic and Protestant.
The work on the Papacy was a reply to Jacob Heilbrunner (1548–1618), a Lutheran court theologian;[2] it comprised a collection of answers to objections of Protestants.