Answer:
The first people who settled what is now Russia and Ukraine were the Eastern Slavs. To some extent it was also the Finnic populations from the north.
Step-by-step explanation:
Three modern countries claim the Kievan Rus as their ancestors, Russia, Ukraine and Belarus.
Between the 9-13th centuries, nomadic slavs began to form unified villages and towns. It was led by the Slavic Prince Oleg.
Eventually by the 13th century a modern Kievan Rus was established. It was a loose federation of various eastern Slavic people who became very powerful in the region.
Their power declined but the development a unique culture and language eventually gave rise to the mighty Russian Empire.