Nikolaus Von Amsdorf, a German reformer, bishop of Naumburg, born near Wurzen, Saxony, Dec. 3, 1483, died at Eisenach, May 14, 1505. He was educated for the church, and early acquired distinction in theology. He seems to have been the confidant of Luther, and attended him in some of his early trials as a reformer. He was a sort of apostle of the reformation, going to Magdeburg (1524), to Goslar (1528 and 1531), and to the principality of Grubenhagen (1534), as the expounder and defender of the principles of the reformation. He was fond of controversy, and this peculiarity more than once involved him in personal difficulties with his friends. He contended that good works were not only hot necessary, but prejudicial to salvation. In the attempt to secure concord between the Lutherans and the Zwinglians (1536), Amsdorf violently opposed the movement, probably on account of his personal hostility to Melanchthon. In 1542 he was appointed bishop of Naumburg, and was consecrated by Luther, who boasted of the uncanonical manner in which the service had been performed, as he himself says, "without suet, lard, tar, grease, or coals." This involved him in a contest with Von Pflugk, who had been regularly appointed by the chapter to the same office.

Amsdorf was a violent opponent of the Augsburg Interim, and was one of the leaders in the adiaphoristic controversy.