Kievan Rus' begins with the rule (882–912) of Prince Oleg, who extended his control from Novgorod south along the Dnieper river valley in order to protect trade from Khazar incursions from the east and moved his capital to the more strategic Kiev. Sviatoslav I (died 972) achieved the first major expansion of Kievan Rus' territorial control, fighting a war of conquest against the Khazar Empire. Vladimir the Great (980–1015) introduced Christianity with his own baptism and, by decree, that of all the inhabitants of Kiev and beyond. Kievan Rus' reached its greatest extent under Yaroslav I (1019–1054); his sons assembled and issued its first written legal code, the Rus' Justice, shortly after his death. 

The term "Kievan Rus'" (Ки́евская Русь Kievskaya Rus’) was coined in the 19th century in Russian historiography to refer to the period when the centre was in Kiev. In English, the term was introduced in the early 20th century, when it was found in the 1913 English translation of Vasily Klyuchevsky's A History of Russia, to distinguish the early polity from successor states, which were also named Rus. Later, the Russian term was rendered into Belarusian and Ukrainian as Кіеўская Русь Kijeŭskaja Rus’ and Ки́ївська Русь Kyivs'ka Rus’, respectively.
how did he do it?
Vladimir the Great (980–1015) introduced Christianity with his own baptism 