 This traditional dating has been challenged by some historians , who point out that it is inconsistent with such other sources as the Schechter Letter , which mentions the activities of certain khagan HLGW of Rus ' as late the 940s , during the reign of Byzantine Emperor Romanus I. The nature of Oleg 's relationship with the Rurikid ruling family of the Rus ' , and specifically with his successor Igor of Kiev , is a matter of much controversy among historians . 
