On an interesting side note, the Romanov's never really had decided claim to the throne. They were not decendents of the first ruler of Russia, Rurik. Instead, the first Romanov was the brother of Anastasia Romanova who was the first wife of Ivan the Terrible.

It was after the title of Tsar had passed through about three other people that claimed to be heir that Michael Romanov took the throne in 1613, 29 years after Ivan the Terrible died of supposed mercury poisoning.