Oleg I of Chernigov
Oleg Svyatoslavich ( or ;  1052 – 1 August 1115) was a Sviatoslavichi prince whose equivocal adventures ignited political unrest in Kievan Rus' at the turn of the 11th and 12th centuries. He reigned as Prince of Chernigov from 1097 to 1115, and was the progenitor of the Olgovichi family. Early life and family 
Oleg was a younger son of Sviatoslav Iaroslavich, Prince of Chernigov and his first wife, Killikiya. He might have been either the second or the fourth among the four sons of Sviatoslav Iaroslavich by Killikiya, because their order of seniority is uncertain. According to historian Martin Dimnik, Oleg was born around 1050. Oleg was named after his grand uncle. His baptismal name was Michael. The Tale of Igor's Campaign styles him Gorislavich, poetically deriving his patronymic from the Russian word for sorrow. His descendants, known as Olgovichi, were archrivals of Vladimir's descendants (known as Monomakhovichi) in their struggle for supremacy in Rus'. Oleg's children were:
 Vsevolod II of Kiev
 Igor II of Kiev
 Maria
 Gleb
 Sviatoslav Olgovich. Military career 
Dimnik writes that "it is highly probable" that Oleg succeeded his brother, Gleb in Tmutarakan after their father appointed the latter Prince of Novgorod in about 1068. Oleg's father and uncle, Vsevolod Iaroslavich made an alliance against their elder brother, Iziaslav Iaroslavich, Grand Prince of Kiev and dethroned him on 22 March 1073. According to Dimnik, Oleg received the Principality of Vladimir from his father who succeeded Iziaslav Iaroslavich in Kiev. In short, Oleg and his cousin, Vladimir Monomachson of Vsevolod Iaroslavichbecame close friends. Monomach writes in his Instruction that Oleg was the godfather of his eldest son, Mstislav. The two cousins together commanded the troops Oleg's father sent to assist Boleslav II of Poland in Bohemia in 1076, according to the Russian Primary Chronicle. Sviatoslav Iaroslavich died in Kiev on 27 December 1077. He was succeeded by his brother, Vsevolod Iaroslavich. The new grand prince seems to have confirmed Oleg's rule in Vladimir, because no source makes mention of a conflict between them. However, the dethroned Iziaslav IaroslavichVsevolod's brother and Oleg's unclereturned with Polish reinforcements. Iziaslav and Vsevolod had a meeting where they reached an agreement: Vsevolod renounced of Kiev, but received Chernigov, the one-time domain of Oleg's father. Iziaslav marched in Kiev on 15 July 1077, while Oleg "was with Vsevolod at Chernigov", according to the Primary Chronicle. The chronicler's remark suggests that Oleg had by that time been forced to leave Vladimir. Failing to get along with his uncle, on 10 April 1077 Oleg fled to his brother Roman who reigned in Tmutarakan. Together with his cousin, Boris Vyacheslavich, who had also settled in Tmutarakan, Oleg made an alliance with the Cumans and invaded Rus' in the summer of 1078. They routed their uncle, Vsevolod on the Sozh River and entered Chernigov on 25 August. The Russian Primary Chronicle accuses Oleg and Boris of being the first to lead "the pagans to attack the land of Rus'". However, Vladimir Monomach, in his Instruction, reveals that he and his father, Vsevolod had hired Cumans when attacking Polotsk in the previous year. Expelled from Chernigov, Vsevolod fled to Kiev and sought assistance from his brother, Iziaslav. They united their forces and marched against Chernigov. Although Oleg and Boris were not in the town when their uncles arrived, the citizens decided to resist. Oleg was willing to start negotiations with his uncles, but Boris refused his proposal. The decisive battle was fought "at a place near a village on the meadow of Nezhata" on 3 October. He was defeated and escaped to Tmutarakan, where the Khazars had him imprisoned and sent in chains to Constantinople. The emperor, who was a relative and ally of Vsevolod, exiled him to Rhodes. There he married a noble lady, Theophano Mouzalonissa, who bore him several children. Chernigov war of succession 
Four years later, sources again find him active in Tmutarakan, where he adopted the title "archon of Khazaria". There ensued a prolonged internecine struggle with his cousins Sviatopolk II Iziaslavich and Volodimer II Monomakh. The war broke out due to the death (13 April 1093) of Vsevolod I Yaroslavich, grand prince of Kiev, and prince of Chernigov and Pereyaslavl. Sviatopolk inherited the throne of Kiev as the eldest son of the senior branch; all parties accepted his accession, but they disagreed which branch would succeed him. The three warring factions were related dynastic princely branches, each descended from three sons of Yaroslav the Wise, and each of whom had reigned as grand prince of Kiev:
 Iziaslavichi, descended from Iziaslav I (; 1076–1078)
  Sviatopolk II Iziaslavich of Kiev. Monomakhi: descended from Vsevolod I ()
  Volodimer II Monomakh of Pereyaslavl
 Izyaslav Volodimirovych of Murom
 Sviatoslavichi: descended from Sviatoslav (; legitimacy disputed)
  Oleg I Sviatoslavich of Chernigov
  Davyd Sviatoslavich of Smolensk 

While he was still alive, Vsevolod had appointed his son Volodimer Monomakh as governor over Chernigov, while the Sviatoslavichi probably still controlled the eastern half of Chernigov centred around Murom (split off as the Principality of Murom decades later). Although Oleg's father Sviatoslav II had reigned as grand prince of Kiev from 1073 until his death in 1076, he had seized power out of order by driving out is brother Iziaslav I. However, the latter regained the Kievan throne from 1076 until his death in 1078, to be succeeded by their youngest brother Vsevolod. While Sviatoslav's sons, the Sviatoslavichi (including Oleg), considered their father's reign to have been legitimate, Vsevolod's son Volodimer Monomakh regarded it as illegitimate. Upon Vsevolod's death, Monomakh therefore refused to hand over Chernigov to the sons of Sviatoslav II of Kiev, and even appointed his own son to govern Murom. Oleg decided to aggressively press his claim to Chernigov, and in 1094, he returned from Tmutarakan with an armed force of Kipchaks to Rus', drove out Monomakh and captured Chernigov. While Monomakh resettled in Pereyaslavl, his sons still controlled eastern Chernigovia, including Murom on the river Oka, resisting Oleg. A 1096 campaign by Oleg succeeded in killing Monomakh's son Iziaslav in Murom, but when he invaded Rostov-Suzdal (a Pereyaslavl possession), he was pushed back to Murom by Monomakh's other son Mstislav. The war ended with a compromise agreement at the 1097 Council of Liubech. Reign in Chernigov 
One of the most prominent princes of Kievan period who never attained the Kievan throne, he died on 1 August 1115, and was buried in Chernihiv. References

Sources

 

The Russian Primary Chronicle: Laurentian Text (Translated and edited by Samuel Hazzard Cross and Olgerd P. Sherbowitz-Wetzor) (1953). Medieval Academy of America. . 1050s births
1115 deaths
11th-century princes from Kievan Rus'
12th-century princes from Kievan Rus'
Eastern Orthodox monarchs
Princes of Tmutarakan
Year of birth uncertain
Sviatoslavichi family
Princes of Chernigov