Vladimir (in Ukrainian, Volodymyr) I, Prince of Kiev, in German Valdimar, in Russian known as Saint Vladimir or as Vladimis the Great, (c.958-1015), was the illegitimate son of Sviatoslav I and the grandson of Olga of Kiev. Varangian ruler of Kiev from 980, he converted to Christianity in 988, reversing Sviatoslav's adherence to the pagan tradition (which was probably a mix of Norse and Slavic elements).

Transferring his capital to Pereyaslavets in 969, Sviatoslav designated Vladimir ruler of Novgorod but gave Kiev to his legitimate son Yaropolk. After Sviatoslav's death (972), civil war erupted (976) between Yaropolk and his younger brother Oleg, ruler of Dereva. As he belonged to the Norse elite, Vladimir fled (977) to Scandinavia, and Novgorod fell to Yaropolk.

Returning in 978 with a large force of Varangian (Viking) warriors, Vladimir recaptured Novgorod the following year. He slew prince Ragnvald of Polotsk and married his daughter Ragnilda, who was engaged to Yaropolk. Yaropolk fled as Vladimir besieged Kiev, but was killed (980) after surrendering to Vladimir, who now ruled all his father's domains.

Though Christianity had won many converts since Olga's rule, Vladimir had remained pagan, taking several wives and erecting pagan statues and shrines to gods, such as Thor and Odin. He continued his efforts to extend his territories, fighting in Galicia in 981, against the Yatvingians on the Baltic coast in 983, against the Bulgars in 985 and against the Byzantine Empire successfully in the Crimea in 987.

In 988 he negotiated for the hand of the Byzantine emperor Basil II's sister, Anna. At Basil's insistence, Vladimir was baptized at Kherson, married Anna and gave up his other wives. Handing over Kherson to the Greeks, he destroyed pagan monuments and established many churches.

Yaroslav, Vladimir's son by an earlier marriage, rebelled against him and refused to render him service or tribute for Novgorod. Vladimir prepared to take Novgorod by force, but died before the attack could begin.

Eastern Orthodox churches celebrate the feast day of the canonised Vladimir on 15 July.

Preceded by:
Rulers of Kievan Rus Succeeded by:
Sviatopolk I