Oleg (Ѡлегъ, Ольгъ; Helgi; died 912), known as Oleg the Wise, Oleg of Novgorod, or Oleg of Kiev, was a Varangian prince of the Rus' who became prince of Kiev and laid the foundations of the Kievan Rus' state.
According to the Primary Chronicle, he succeeded his "kinsman" Rurik as ruler of Novgorod, and subdued many of the East Slavic tribes to his rule, extending his control from Novgorod to the south along the Dnieper river. Oleg also launched a successful attack on Constantinople. He died in 912 and was succeeded by Rurik's son, Igor.
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 a certain khagan HLGW (הלגו usually transcribed Helgu. Compare Swedish first name Helge.) of Rus' as late as 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.
According to the Primary Chronicle, Oleg was a "relative" or "kinsman" of Rurik, and was entrusted by Rurik to take care of both his realm and his young son Igor. However, his relation to Rurik is debatable, and has been rejected by several modern scholars. Oleg is narrated to have succeeded Rurik as the ruler of Novgorod in 879. In 881/882, he took control of Smolensk, and then seized power in Kiev by tricking and slaying Askold and Dir, and setting himself up as prince in Kiev, which is commonly taken as the founding of Kievan Rus'. Although Oleg was the first "prince" (knyaz) of Kiev according to the Primary Chronicle, he was not yet a "grand prince" (velikiy knyaz). Whereas later Muscovite chroniclers would call Oleg a "grand prince" and Kiev a "grand principality" (великое княжение), the earliest sources do not.
In 883, Prince Oleg of Novgorod made the Drevlians pay tribute to Kiev.