Jonas, Justus one of the most eminent reformers in Germany, a contemporary and associate of Luther. was born at Nordhausen, June 5,1493. He studied law at the University of Erfurt. In 1519, however, encouraged by the advice of both Hess and Erasmus, he decided to study theology, and, inclining to the cause of the Reformers, he allied himself to Luther in 1521, and thereafter became closely connected with the great reformer. He went to Worms with him, and was soon after appointed provost of the church at Wittenberg. Here he was made D.D. by the university, in which he became a professor, and ever after worked zealously for the propagation of the principles of the Reformation. His legal knowledge was of especial service to the Reformers. In 1529 he accompanied Luther to Marburg, and his letters on this occasion are a valuable historical contribution. In 1530 we find him assisting Melancthon in the completion of his Augustana. In 1541 he removed to Halle to assume pastoral duties at St. Mary's Church in that city, but in 1546 duke Maurice ordered him to quit the place, and he returned only after the elector John Frederick had taken possession of the city in 1547. The battle of Mühlberg, which falls in this year, again turned the fate of the Protestants, and he once more quitted Halle. In 1551 he was appointed court preacher at Coburg, and in 1553 superintendent of Eisfeld, where he died Oct. 9, 1555. Jonas was particularly distinguished as a ready speaker and as a writer. He took part in the translation of the Bible by Luther, and wrote Proefatio in Epistolas divi Pauli Apostoli, ad Corinthios, etc. (Erfurt, 1520, 4to): — Epitome Judicii J. Jonoe, proepos. Wittemb., de corrigendis coerimoniis (1523): — Annotationes J. Jonoe in Aeta Apostolorum (Wittenb. 1524, Basle, 1525): — Vom alten u. neuen Gott, Glauben u. Lehre (Wittenb. 1526): — Welch die rechte Kirche, und dagegen welch d. falsche Kirche ist (Wittenb. 1534, 4to): — Oratio Justi Jonoe, doct. theol., de Studiis Theologicis (Wittemb. 1539; Melancthon, Select. Declamat. 1, 23): Des 20 Psalms Auslegung (Wittemberg, 1546): — Kurze Historia v. Luthers biblischen u. geistlichen Anfechtungen (in Luther's Works); etc. He also published a number of translations into German, especially of works of Luther and Melancthon; also translations from German into Latin. See Reinhard, Commentatio hist. theolog. de Vita et Obitu Justi Jonoe, etc. (Weimar, 1731); Knapp, Narratio de Justo Jona, etc. (Halle, 1817; 4to): Ersch u. Gruber, Allgemeine Encyklop.; Herzog, Real-Encyklop. 7, 1 sq.; Pressel, Leben u. ausgew. Schriften d. Vaters u. Begründers. d. luther. Kirche (1862), vol. 8.