Peter III of Russia
During the 18th Century, the Dukes of Holstein-Gottorp gained influence through a carefully planned series of marital alliances with the royal houses of Germany, Denmark, Sweden, Norway and Prussia. The childless Empress Elizabeth of Russia proclaimed her nephew, Charles Peter Ulrich of Holstein-Gottorp heir to the throne and when he became Emperor Peter III of Russia in 1762, the Holstein-Gottorps, themselves a cadet branch of the House of Oldenburg, became the Imperial house of Russia, which they ruled until 1917 under the name of Romanov.