Mongol leader and khan of the Golden Horde, or Kipchak empire, of southern Russia, under whom it attained its greatest power; he reigned from 1312 to 1341. Öz Beg was a convert to Islām, but he also welcomed Christian missionaries from western Europe into his realm. Öz Beg encouraged the predominance of the princes of Moscow among his Christian vassals; his name survives today in that of the Uzbek people and of Uzbekistan.