Tsar of Russia (1598–1605). He began his career of court service under Ivan IV (the Terrible), became virtual ruler of Muscovy during the reign of his imbecile son Fyodor (1584–98) and engineered his own elevation to the Tsardom. He conducted a successful war against Sweden (1590–95), promoted foreign trade, and dealt ruthlessly with those boyar families which opposed him. In 1604 boyar animosity combined with popular dissatisfaction ushered in the ‘Time of Troubles’—a confused eight-year dynastic and political crisis, Boris having died suddenly in 1605.