Askold and Dir
According to the "Primary Chronicle", Oleg was a relative (likely brother-in-law) of the first ruler, Rurik, and was entrusted by Rurik to take care of both his kingdom and his young son Igor. Oleg gradually took control of the Dnieper cities, seizing the power in Kiev by tricking and slaying Askold and Dir, and naming Kiev the capital of his newly created state Kievan Rus'. The new capital was a convenient place to launch a raid against Constantinople in 907.