Rurik (or Ryurik), a semi-legendary Scandinavian Varangian, was at the roots of Kievan Rus'. He founded the Rurikovich dynasty that would rule Kievan Rus', Rus' principalities and early Russian Tsardom for the next 700 years. Rurik's capital was the northern city of Novgorod. His successor Oleg relocated the capital to Kiev at around 880, thus laying the foundation of what has become known as Kievan Rus'.
While the early rulers of Rus' were Scandinavians, they gradually merged into the local Slavic population. Still, in the 11th century, Yaroslav, (called Jarisleif in Scandinavian chronicles) maintained the dynastic links, married a Swedish princess, and gave asylum to king Olaf II of Norway.
The movement of nobility also went in the opposite direction. According to Adam of Bremen, Anund Gårdske, a man from Kievan Rus' was elected king of Sweden, ca 1070. As he was a Christian, however, he refused to sacrifice to the Aesir at the Temple at Uppsala and he was deposed by popular vote.
The unity of Kievan Rus' gradually declined, and was all but gone by 1136. After that period Kievan Rus' shattered into a number of smaller states, southern of which contested for the throne of Kiev.