Peter III of Russia

Born a German duke as Charles Peter Ulrich of Schleswig-Holstein-Gottorp, he lost his mother to childbirth fever and inherited Holstein-Gottorp after his father's death. In 1742 he was named heir to both the Russian and Swedish thrones, but his forced conversion to Russian Orthodoxy disqualified him from Sweden. He married his second cousin Sophie of Anhalt-Zerbst in 1745; she became Catherine, and they had one surviving son, Paul. When Peter succeeded his aunt as Emperor of Russia on 5 January 1762, he pushed through notable reforms but enraged the military by ending the Seven Years' War and allying with Prussia, abandoning hard-won Russian gains. On 9 July his wife overthrew him in a palace coup. Nine days later he was dead, the cause officially listed as hemorrhoids - a claim greeted with open disbelief across Europe. His shadow lived on in a parade of impostors, most famously the rebel Yemelyan Pugachev, who nearly tore the empire apart claiming to be the murdered tsar.