When in 1015 his father died, strife occurred between Jaroslav and his brothers. Svyatopolk, the eldest, murdered Boris, Gleb and Syvatoslav and then was driven out by Jaroslav. Of the other brothers, Izyaslav remained safe in Polotzk, Sudislav was imprisoned while Mstislav in Tmutorokan prevented Jaroslav, until 1036, from being an absolute ruler as their father had been. Boris and Gleb were venerated as the first Russian saints.
Jaroslav, like his father, ruled for thirty-five years. He brought prosperity while the arts and literature flourished and in Kiev the cathedral of St. Sophia was built. In 1030 he conquered Estonia and a year later, with his brother Mstislav's support, attacked Poland.
Mstislav died in 1036 leaving Jaroslav as the sole ruler. At last he defeated the Pechenegs and in the ensuing peace Christianity flourished and new monasteries were built. Before his death he divided
his lands between his five sons.
 

Source: Leo van de Pas