You probably have never heard of
The reformer Urbanus Rhegius (Koenig)[. He] was born in 1490 at Langenargen, near Lindau. He studied at Freiburg and at Ingolstadt. At the latter place he became professor of poetry and rhetoric. In the year 1520, he became cathedral preacher at Augsburg, where he accepted the principles of the Reformation. In 1530, he was called as superintendent to Celle and as such was the reformer of the Duchy of Luncburg. He died March 23, 1541. His works appeared in 1562 at Nuremberg, four volumes in German, three volumes in Latin. His biography was written by Heimbuerger (Gotha, 1851) and by Uhlhorn (Elberfeld, 1861).*
As was the case of many in those heady days, Rhegius frequently sought Zwingli’s advice concerning theological questions, particularly on the topic of original sin. It was to Rhegius that Zwingli dedicated his book on that very subject.
As the editor of the English edition notes
This pamphlet was in answer to a letter of Rhegius to Zwingli, which has not been discovered thus far. (See Zwingli’s Werke, Vol. VIII. (1914), 633, note 4). Rhegius had some doubts as to the soundness of Zwingli’s views regarding original sin. This appears from a letter which he wrote on January 14, 1526, to Ambrose Blaurer of Constance, in which he expressed himself rather vigorously: “I am sorry Zwingli was not at Baden [i. e., the Baden Disputation, May 21–June 18, 1526]. He would have defeated all the Papists once for all, except in the matter of original sin, which he seems to treat in a very unsound fashion. In regard to the Lord’s Supper, though he might be criticized, he certainly could not have been defeated by those counterfeit theologians.” Nor was his mind altogether set at rest by this treatise, for he expresses in a letter of September 28, 1526 (Zwingli’s Werke, VIII, 726–8) the fear that Zwingli might be accused of Origenism. Zwingli tried to remove his doubts by a letter dated October 16, 1526 (Werke, VIII, 737–9).]*
Rhegius and Zwingli remained on excellent terms throughout the latter’s life, in spite of their differences on this singular issue (just as Zwingli and I remain on excellent terms in spite of his inaccurate views on baptism).
More on Rhegius is available in Maximilian Liebmann, Urbanus Rhegius und die Anfänge der Reformation, Beiträge zu seinem Leben, seiner Lehre und seinem Wirken bis zum Augsburger Reichstag von 1530 mit einer Bibliographie seiner Schriften, Münster 1980 (Reformationsgeschichtliche Studien und Texte 117).
*The Latin Works of Huldreich Zwingli. (W. J. Hinke, Ed.) (Vol. 2).