Michael I of Russia (Russian: Михаил Фёдорович Романов, Mikhail Fyodorovich Romanov) became the first Russian Tsar of the House of Romanov after the zemskiy sobor of 1613 elected him to rule the Tsardom of Russia. He was the son of Feodor Nikitich Romanov (later known as Patriarch Filaret) and of Xenia (later known as "the great nun" Martha). He was also a nephew of Feodor I (the last Rurikid Tsar) through his great-aunt Anastasia Romanovna (his paternal grandfather's sister) and through marriage with Tsar Ivan IV of Russia. His accession marked the end of the Time of Troubles. During his reign, Russia conquered most of Siberia, largely with the help of the Cossacks and the Stroganov family. Russia had extended to the Pacific Ocean by the end of Michael's reign.