Oleg of Kiev was a prominent ruler of the East Slavs in the late 9th and early 10th centuries. He is best known for uniting various Slavic tribes and establishing the Kievan Rus', a federation that laid the foundation for modern Ukraine, Belarus, and Russia. Oleg is often credited with expanding trade routes and strengthening the region's economy. Oleg's reign is marked by military conquests, including the capture of Constantinople in 907 AD, which solidified his power and influence. He is also remembered for his diplomatic relations with the Byzantine Empire, which helped to enhance the cultural and political landscape of the region.