Ernest I, widely known as Ernest the Pious, was duke of Saxe-Gotha and Saxe-Altenburg, later united as Saxe-Gotha-Altenburg. He was a surviving son of Johann II, Duke of Saxe-Weimar and Dorothea Maria of Anhalt. He is remembered for rebuilding and reforming his lands after the Thirty Years' War. A devout Lutheran, he allied with Sweden in 1631 and fought at Lech, Nördlingen, Lützen, and the siege of Nuremberg; after the Peace of Prague (1635) he withdrew from warfare to focus on administration and recovery.