 According to the Primary Chronicle , Oleg died in 912 and his successor , Igor of Kiev , ruled from then until his assassination in 945 . The Schechter Letter , a document written by a Jewish Khazar , a contemporary of Romanus I Lecapenus , describes the activities of a Rus ' warlord named <unk> ( Hebrew : <unk> ) , usually transcribed as " Helgu " . For years many scholars disregarded or discounted the Schechter Letter account , which referred to Helgu ( often interpreted as Oleg ) as late as the 940s . 
