German duke, as the tenth but seventh surviving son of Ernst I, Duke of Saxe-Gotha and Elisabeth Sophie of Saxe-Altenburg.
After the death of his father in 1675, Johann Ernst initially governed the duchy of Saxe-Gotha-Altenburg, jointly with his six older brothers, as set out in their father’s will. However, in 1680, the brothers concluded a treaty dividing the paternal lands and Johann Ernst became duke of Saxe-Saalfeld, with the towns of Gräfenthal, Probstzella and Pössneck. As he was the youngest, he kept the smallest portion of the lands.
Johann Ernst and his brother Ernst soon found themselves financially overstretched as a result of the partition (the income of their eldest brother, Friedrich, far exceeded the income of Johann Ernst), and they both made a protest. Over the following years, the controversy continued and increased, as their older brothers Albrecht of Saxe-Coburg, Heinrich of Saxe-Römhild and Christian of Saxe-Eisenberg died without male heirs. During these years, Johann Ernst took possession of Coburg (in 1699), Römhild and 5/12 of Themar (in 1714).
The “Coburg-Eisenberg-Römhilder Erbstreit” was finally resolved (after repeated intervention and arbitration by the emperor) in 1735, six years after the death of Johann Ernst. His descendants retained Coburg. The decision was generally accepted, most importantly by the descendants of his older brother Bernhard, who also had a claim to Coburg.
Johann Ernst married twice and had thirteen children. He died on 17 February 1729, aged 70, in Saalfeld.
Link to Wikipedia biography