Final answer:
Prince Vladimir I of Kiev led the early Russian state to its apex of power and prestige, fostering religious transformation by converting to Orthodox Christianity and forming an alliance with the Byzantine Empire.
Step-by-step explanation:
The city of Kiev and the early Russian state reached the height of their power and prestige under the leadership of Prince Vladimir I of Kiev. Vladimir, who reigned from around 980 to 1015 CE, was a transformative figure whose conversion to Orthodox Christianity in 988 led to the Christianization of Kievan Rus'. His marriage to Byzantine Emperor Basil II's sister Anna solidified his significant alliance with the Byzantine Empire. Prince Vladimir's reign brought not only religious transformation but also cultural development, as Kievan Rus' began appropriating and adapting Byzantine art and architecture.
Furthermore, through his vigorous military conquests, Vladimir united the Rus' people and extended the influence of Kievan Rus' across Eastern Europe. His dedication to spreading Orthodox Christianity earned him the title The Holy and later canonization in the Orthodox Church. Prince Vladimir's legacy can be seen today, with statues commemorating him in both Moscow, Russia, and Kiev, Ukraine, reflecting his enduring impact on the region.