High Quality Content by WIKIPEDIA articles! John Casimir of the Palatinate-Simmern (German: Johann Casimir von Pfalz-Simmern) (7 March, 1543 – 16 January 1592) was a German prince and a younger son of Elector Frederick III, Count Palatine of the Rhine. A firm Calvinist, he was a leader of mercenary troops in the religious wars of the time, including the Dutch Revolt. From 1583–1592 he acted as regent for his nephew, Elector Frederick IV.