From the LCMS website:
Martin Chemnitz (1522–1586) is regarded after Martin Luther as the most important theologian in the history of the Lutheran Church. Chemnitz combined a penetrating intellect and an almost encyclopedic knowledge of Scripture and the church fathers with a genuine love for the church. When various doctrinal disagreements broke out after Luther’s death in 1546, Chemnitz determined to give himself fully to the restoration of unity in the Lutheran Church. He became the leading spirit and principal author of the 1577 Formula of Concord, which settled the doctrinal disputes on the basis of the Scriptures and largely succeeded in restoring unity among Lutherans. Chemnitz also authored the four volume Examination of the Council of Trent (1565–1573), in which he rigorously subjected the teachings of this Roman Catholic Council to the judgment of Scripture and the ancient church fathers. The Examination became the definitive Lutheran answer to the Council of Trent, as well as a thorough exposition of the faith of the Augsburg Confession. A theologian and a churchman, Chemnitz was truly a gift of God to the Church.