Emmanuel Augustin Dieudonne Las Cases, seigneur de la Caussade and count de, a French historian, and companion of Napoleon at St. Helena, born at the chateau of Las Cases, near Revel, Languedoc, in 1766, died at Passy-sur-Seine, May 15, 1842. He was educated at the school of the Oratorians in Vendome, and at the military and naval schools of Paris, and served in the navy, becoming lieutenant at the age of 21. When the revolution broke out he took part with the royalists, emigrated, and was employed by the prince of Conde in many diplomatic missions, among others to Gustavus III. of Sweden, then at Aix-la-Chapelle, who became his friend. After the defeat of the Prussians in Champagne he fled to London, where he supported himself by teaching. When the emigres were recalled by Napoleon, Las Cases returned to Paris, and for some time lived in obscurity. But he was appointed chamberlain of the emperor in 1808, and in 1809 entered the army of Bernadotte. In 1810 he was appointed master of requests in the council of state, and in 1811 intrusted with the liquidation of the Austro-Illyrian debt.

In 1812 he was appointed inspector of prisons, hospitals, and similar institutions, and of all the ports and naval stations from Toulon to Amsterdam. After the disasters of Moscow and Leipsic, Las Cases commanded the 10th legion of the national guard. In 1814 he opposed Napoleon's abdication, and went to England, whence he subsequently sent in his adhesion to the Bourbons. After the return from Elba he went back to France, and after Waterloo followed Napoleon to St. Helena. Here with his son he devoted himself to the care of the emperor, and passed his evenings in recording his remarks. Having written a letter to Lucien Bonaparte commenting on the treatment to which Napoleon was subjected, he was arrested, Nov. 27, 1816, and sent to the Cape of Good Hope, where he was confined eight months. He was taken to England, but not suffered to land, and afterward conducted to Frankfort, where he at last received his liberty after 13 months' captivity. He afterward resided in Belgium, but it was not until the death of Napoleon that he was allowed to return to France. He now published his St. Helena notes, which are said to have yielded him 2,000,000 francs. He was elected in 1831 and 1839 to the chamber of deputies, taking his seat with the ultra opposition.

Besides his Memorial de Sainte-Helene (8 vols., 1822-'3), he composed an Atlas historique et geogra-phique (1803-4), and an autobiography entitled Memoires d'E. A. D., comte de Las Cases, communiques par lui-meme (1819).