Vladimir the Great, also known as Vladimir I of Kiev, was a ruler of Kievan Rus' from 980 to 1015. He is best known for uniting the various Slavic tribes and expanding the territory of his state. Under his leadership, Kievan Rus' became a significant political and cultural center in Eastern Europe. One of Vladimir's most notable achievements was the Christianization of Kievan Rus'. In 988, he adopted Christianity as the state religion, which helped to strengthen ties with the Byzantine Empire and fostered cultural development. His reign laid the foundation for the future of Eastern Orthodox Christianity in the region.