Boyar
A boyar was a member of the ruling nobility in medieval Russia and some other Slavic countries such as Bulgaria.  The boyars held the most important jobs in the army.  They met in a group called the duma and gave advice to the ruling prince or, in later times, the tsar.  In the 13th and 14th centuries they were rich landowners who could advise the prince, but they were free to go and work for another prince if they wanted to.