PETER III. (1728-1762), emperor of Russia, only son of Charles Frederick, duke of Holstein-Gottorp, and of Anne, eldest surviving daughter of Peter the Great, was born at Kiel on Feb. 21, 1728. In December 1741 he was adopted by his aunt, Elizabeth Petrovna, as soon as she was safely established on the Russian throne, and on Nov. 18, 1742 was received into the Orthodox Church, exchanging his original name of Karl Peter Ulrich for that of Peter Fedorovich. On Aug. 21, 1745, by the command of his aunt, he married the princess Sophia Augusta Frederica of Anhalt-Zerbst (Catherine Alekseyevna). The union between a prince who physically was something less than a man and mentally little more than a child, and a princess of prodigious intellect and an insatiable love of enjoyment, was bound to end in catastrophe. But there is no foundation for the stories of Peter's neglect and brutality. Even when Peter III. succeeded Elizabeth on Jan. 5, 1762, he paid off Catherine's debts, without inquiring their origin. He gave her a magnificent establishment and great domains. His infidelities Catherine took as a matter of course, provided her own love affairs were not interfered with.
Peter's foreign policy reversed that of Elizabeth. He had not been on the throne for two months when he made pacific over tures to the king of Prussia, whom he habitually alluded to as "the king my master." Peter's worship of Frederick resulted in
a peace (May 5) and then ( June 19) in an offensive and defensive alliance between Russia and Prussia, whereby Peter restored to Prussia all the territory won from her by Russia during the last five years, and engaged to defend Frederick against all his enemies. This was followed up by a whole series of menacing rescripts addressed by Peter to the court of Vienna, in which war was threatened unless Austria instantly complied with all the demands of the king of Prussia. Finally he quarrelled with Denmark, and the Russian army received orders to invade Den mark by way of Mecklenburg. But before the actual collision took place news came of the coup d'etat at St. Petersburg, by which Catherine (see CATHERINE II.) succeeded to the throne of Russia. From July 9 to July 18 Peter was in custody at the castle of Ropsha. His end is uncertain, but the evidence points to his murder (July 18, 1762) by Alexius Orlov, Theodore Baryatinski, and several other persons still unknown.
See R. N. Bain, Peter III., Emperor of Russia (London, 1902) ; V. A. Bilbasov, History of Catherine II. (Rus.), vol. i. (Berlin, 1900). (R. N. B.)