Askold and Dir
Circa AD 800, the Varangians Askold and Dir organised an army and travelled down the Dnieper to Kiev in order to save the cities inhabitants from a besieging tribe. In doing so, they paved the way for the ascension of the Rurik dynasty over not just Kiev and Novgorod, but all the tribes that make up the East Slavs. The Varangians brought these Slavic tribes political cohesion by building one of the most powerful medieval kingdoms, and undoubtedly a sense of cultural cohesion with the conversion of Rus to Christianity in AD 988.