LOUDON, ERNST GIDEON, FREIHERR VON 1790), Austrian soldier, was born on Feb. 2, 1717, at Tootzen, Livonia, where his family, of Scottish origin, had been settled since before 1400. His father had been in the Swedish service; the boy entered the Russian army as a cadet in 1732, saw service in 1735, and 1738-39, then resigned (1741), and after vainly apply ing for employment with Frederick the Great, became a captain in Trenck's corps in Vienna. Soon after the outbreak of the Seven Years' War he became colonel, in 1757 major-general of cavalry, and in 1758 forced Frederick to raise the siege of Olmiitz. In 176o he won a further victory at Kunersdorf, was promoted f eldzeug meister and made commander-in-chief in Bohemia, Moravia and Silesia.
He was successful at Landshut and Glatz, but was defeated by Frederick at Liegnitz (Aug. 15, 176o), which action led to bitter controversy with Daun and Lacy, the commanders of the main army, who, Loudon claimed, had left his corps unsupported. In 1761 he operated again in Silesia, but was hampered by the inac tivity of his Russian allies. (See SEVEN YEARS' WAR.) His tireless activity continued to the end of the war, in conspicuous contrast with the temporizing strategy of Daun and Lacy, and led in the last three years of the war to ever-increasing friction between the "Fabius" and the "Marcellus," as they were called, of the Austrian army.
After the peace dissensions continued between Loudon and Lacy, and Loudon only remained in the army at the special request of Maria Theresa, acting as commander-in-chief in Bohemia and Moravia 1769-72. In 1776 he settled at Hadersdorf near Vienna, and was made a field-marshal in Feb. 1778.
In the same year he was reconciled with Joseph II. and Lacy and commanded one of the two armies in the field in the war of the Bavarian Succession, but this time with only moderate suc cess. He then retired again to Hadersdorf ; but recalled after the reverses of the other generals in the Turkish War, he was made commander-in-chief, and won a last brilliant success by capturing Belgrade in three weeks, 1789. He died on July 14 at Neu Titschein in Moravia, still on duty. His last appointment was that of commander-in-chief of the armed forces of Austria, which had been created for him by the new emperor Leopold. Loudon was buried in the grounds of Hadersdorf.
See memoir by v. Arneth in Allgemeine deutsche Biographie, s.v. "Loudon," and life by G. B. Malleson.