Sviatoslav II of Kievan Russia was the son of Yaroslav I
and the brother of Izyaslav I
, who was Grand Prince of Russia in Kiev first, while Sviatoslav was prince of Cherngiv. During his time in his own city, Sviatoslav funded the building and decoration of cathedrals, and tried to implement the rather ascetic version of Orthodox Christianity
preached by the Cherngiv-area monk Feodosii (Theodorius), who was later canonized by the Russian Orthodox Church.
During his brother's early years on the throne, Sviatoslav supported him against usurpers such as Vseslav, but in 1073, Sviatoslav (who had convinced their other brother Vsevolod that Izyaslav was conspiring against them) was able to take over the throne of Kiev and hence the Grand Prince position, while Izyaslav fled Russia. He didn't really accomplish much as Grand Prince, and died suddenly in 1076, which allowed Izyaslav the chance to return to Russia and rule again.