From the LCMS website:
Johann Gerhard (1582–1637) was a great Lutheran theologian in the tradition of Martin Luther (1483– 1546) and Martin Chemnitz (1522–86) and the most influential of the 17th-century dogmaticians. His monumental Loci Theologici (23 large volumes) is still considered by many to be a definitive statement of Lutheran orthodoxy. Gerhard was born in Quedlinburg, Germany. At the age of 15 he was stricken with a life-threatening illness. This experience, along with guidance from his pastor, Johann Arndt, marked a turning point in his life. He devoted the rest of his life to theology. He became a professor at the University of Jena and served many years as the Superintendent of Heldberg. Gerhard was a man of deep evangelical piety and love for Jesus. He wrote numerous books on exegesis, theology, devotional literature, history, and polemics. His sermons continue to be widely published and read.