Yaroslav I, Grand Prince of Rus', known as Yaroslav the Wise or Iaroslav the Wise (Old East Slavic: Ꙗрославъ Володимѣровичъ Мѫдрꙑи; Russian: Яросла́в Му́дрый, translit. Jaroslav Mudryj [jɪrɐˈslaf ˈmudrɨj]; Ukrainian: Яросла́в Му́дрий, translit. Jaroslav Mudryj [jɐroˈslɑu̯ ˈmudrɪj]; Old Norse: Jarizleifr Valdamarsson;; Latin: Iaroslaus Sapiens; c. 978 – 20 February 1054) was thrice grand prince of Veliky Novgorod and Kiev, uniting the two principalities for a time under his rule. Yaroslav's Christian name was George (Yuri) after Saint George (Old East Slavic: Гюрьгi, Gjurĭgì).

A son of Vladimir the Great, the first Christian Prince of Novgorod, Yaroslav acted as vice-regent of Novgorod at the time of his father's death in 1015. Subsequently, his eldest surviving brother, Sviatopolk I of Kiev, killed three of his other brothers and seized power in Kiev. Yaroslav, with the active support of the Novgorodians and the help of Varangian mercenaries, defeated Svyatopolk and became the Grand Prince of Kiev in 1019. Under Yaroslav the codification of legal customs and princely enactments was begun, and this work served as the basis for a law code called the Russkaya Pravda ("Rus Truth [Law]"). During his lengthy reign, Kievan Rus' reached the zenith of its cultural flowering and military power.

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