Oleh Sviatoslavych (baptismal name – Michael; birth place and date unknown – 01.08.1115) – Prince of Volodymyr-Volynsky (1076), Tmutorokan (1083–1094), Chernihiv (1094–1096), and Novhorod-Siversky (1097–1115) from the Riurikid dynasty. The progenitor of the Olhovychi family, son of Grand Prince Sviatoslav Yaroslavych of Kyiv, grandson of Yaroslav the Wise.
From 1076 Oleh Sviatoslavych reigned in Volodymyr-Volynsky. That same year he, together with Prince Volodymyr Monomakh, waged a successful campaign to Czechia to support King Bolesław II the Bold of Poland.
After the death of his father (1076) he lost the Volodymyr-Volynsky throne and lived in Chernihiv as Prince the outcast. In April 1078 run away to his brother Roman to Tmutorokan. In August 1078 Oleh Sviatoslavych (together with Borys Vyacheslavych) brought the Polovtsians to the Rus land. On August 25 a battle against the army of Vsevolod Yaroslavych took place at the River Sozhytsia (now the Orzhytsia). Vsevolod’s army suffered a defeat, Oleh and Borys seized Chernihiv. Princes Vsevolod Yaroslavych with his son Yaropolk and Iziaslav Yaroslavych with his son Volodymyr came out against Oleh and Borys. On October 3, 1078, Borys Vyacheslavych and Iziaslav Yaroslavych died in the battle at Nezhatyna Nyva (now the town of Nizhyn, Chernihiv Oblast). Oleh’s troops suffered a defeat and he was forced to return to Tmutorokan. In 1079 Oleh Sviatoslavych was treacherously caught by the Polovtsians who gave him over to Byzantium. The Byzantine government exiled the Prince to Rhodes Island where he lived for four years. He married there a noblewoman Theophano Mouzalon.
In 1083 he returned and took away the Tmutorokan throne from Davyd Ihorovych and Volodar Rostyslavych. In 1094, supported by the Polovtsians, he got the Chernihiv Principality (according to some information, Prince Volodymyr Monomakh voluntarily gave him Chernihiv in possession). Led a prolonged struggle against Grand Prince of Kyiv Sviatopolk Iziaslavych, Volodymyr Monomakh and his sons Iziaslav and Mstyslav. Their combined troops forced Oleh to leave Chernihiv in 1096. Later, by the decision of the Liubech Congress of 1097 he got the Novhorod-Siversky Principality. In 1107 and 1113 he took part in campaigns against the Polovtsians.
Buried in the Cathedral of Our Saviour in Chernihiv.