Any male member of the upper class of medieval Russian society and state administration. In Kievan Rus (10th–12th centuries) the boyars belonged to the prince's retinue, holding posts in the army and civil administration and advising the prince in matters of state through a boyar council, or duma. In the 13th–14th centuries the boyars constituted a privileged class of rich landowners in northeastern Russia. In the 15th–17th centuries the boyars of Muscovy ruled the country along with the grand prince (later the czar) and legislated through the boyar council. Their importance declined in the 17th century, and the title was abolished by Peter I in the early 18th century.