Ar begs (in Russian chronicles "Арские князья") was a formation of Noqrat Tatars' nobility, served to Muscovy in 16th-17th century. In 14th-15th centuries they were rulers of semi-independent duchy in the middle Cheptsa, nowadays Udmurtia. at the first time, their lands were under Kazan Khanate's and later under Russian influence. Begs also participated in wars for Udmurtia between Kazan and Muscovy.
References
Ar begs Wikipedia(Text) CC BY-SA