George Properly Callisen (Calixtus), a Lutheran divine, born at Meelby in Holstein, Dec. 14, 1586, died in Helmstedt, March 19, 1656. From 1609 to 1613 he travelled through France, England, and Germany, and by this means became acquainted with many of the leading theologians of those countries. On his return the duke of Brunswick appointed him professor of theology in Helmstedt, where he remained for nearly half a century, writing and publishing a large number of theological works, and endeavoring to reconcile and unite the various Christian churches, on the basis of the Apostles' creed. At the conference of Thorn (1645) he showed himself so moderate in his Lutheran opinions as to favor and attempt the reconciliation of the Protestants and the Reformed church, and thereby incurred the hatred of Oalovius and his adherents, who insisted on his excommunication from the Lutheran church as suspected of Calvinism. He had already been accused of Catholicism on account of one of his works, the Epitome Theologice Moralis. On the other hand, the Catholics regarded him as their most sagacious and insidious enemy. He considered a union of the sundered body of Christ feasible, if the conflicting parties could be induced to return to the oecumenical councils and laws of the first five centuries.

This plan gave rise to what is known in ecclesiastical history as Syncretism, though the followers of Calixtus are sometimes called Calix-tines. He had embraced the Aristotelian philosophy, and on that plan he produced scientific systems of ethics and theology. A full list of his writings is given in his Consultatio de Tolerantia Reformatorum (Helmstedt, 1697).