CALIXTUS, Georgius (1586-1656), a celebrated Lutheran divine, born at Middleburg in Holstein in 1586. After studying at Helmstadt, Jena, Giessen, Tübingen, and Heidelberg, he had an opportunity of travelling through France and England, where he became acquainted with the leading Reformers, and saw the different forms which the Reformed church had assumed. On his return he was appointed professor of divinity at Helmstadt by the duke of Brunswick, who had admired his abilities in a contest which he had when a young man with the Jesuit Augustine Turrianus. After becoming a master of arts he published a book, Disputationes de Proecipuis Religionis Christianae Capitibus, which provoked the hostile criticism of several learned men; and on his elevation to the professorship he published his Epitome of Theology, and soon after his Epitome of Moral Theology, which gave so great offence as to induce Statius Buscher to charge him with a secret leaning to Romanism. Scarcely had he refuted the accusation of Buscher, when, on account of his intimacy with the Reformed divines at the conference of Thorn, and his desire to unite them with the Lutherans, a new charge was preferred against him, principally at the instance of Calovius, of a secret attachment to Calvinism. The disputes to which this gave rise, known in the church as the Syncretistic controversy, lasted during the whole lifetime of Calixtus, and distracted the Lutheran Church, till a new controversy arose with Spener and the Pietists of Halle. Calixtus died in 1656. There is a monograph on Calixtus by Henke, 2 vols. 1853-56; see also Dorner, Gesch. d. Protest. Theok, pp. 606-624.