Johann Ernst of Saxe-Eisenach (Gotha, 9 July 1566 – Eisenach, 23 October 1638), was a duke of Saxe-Eisenach and later of Saxe-Coburg. He was the fourth (but second surviving) and youngest son of Johann Frederick II, Duke of Saxony and Countess Palatine Elisabeth of Simmern-Sponheim. His grandfather, Johann Frederick I, had still held the title of Elector of Saxony, but after the Battle of Mühlberg he lost the title to his cousin Maurice, from the Albertine line. His father tried since then to regain the Electorate again for the Ernestine line. For this purpose he accepted an outlawed knight, Wilhelm von Grumbach, with himself, which led finally to the fact that also over his father the anger of the Emperor. Only one year after his birth was besieged the castle of his father in Gotha by troops of the Elector Augustus of Saxony and finally conquered. His father came into imperial prison from the rest of his life. His mother, Johann Ernst and his older brothers had to flee from Gotha. They found first admission with his uncle, the duke Johann Wilhelm of Saxe-Weimar, who took over also the guardianship for the princes -at the same time, he was granted by the Emperor with the lands of his brother Johann Frederick II-. After a short time in Weimar, Johann Ernst, as well as his mother and his brothers, lived in Eisenach and Eisenberg. Later, his uncle Johann Wilhelm of Saxe-Weimar lost the Imperial favour. In the Diet of Speyer (1570), the Emperor decided to restore to the three sons of Johann Frederick II his hereditary rights. In 1572 his older brother Frederick Heinrich died from typhus fever. The same year, by the Division of Erfurt, the decision of the Diet of Speyer was made: The lands of his father were extracted again from the duchy of Saxe-Weimar, and created from them the new Duchy of Saxe-Coburg-Eisenach. Johann Ernst and his older surviving brother, Johann Casimir, were made rulers of the new country. During there minority, the lands were under the guardianship of the three Elector Princes: Frederick III of the Palatinate (also his maternal grandfather), Johann George of Brandenburg and Augustus of Saxony; also, they took the regency over Saxe-Coburg-Eisenach. The duchess Elizabeth moved to Austria, where she should live themselves in the future in the proximity of her husband, still imperial prissioner. The two young princes, Johann Casimir and