Mstislav I Vladimirovich Monomakh (Old East Slavic: Мьстиславъ Володимѣровичъ Мономахъ, romanized: Mĭstislavŭ Volodiměrovičŭ Monomakhŭ;^{[lower-alpha 1]} Christian name: Fedor;^[1][2] February 1076 – 14 April 1132), also known as Mstislav the Great, was Grand Prince of Kiev from 1125 until his death in 1132. After his death, the state began to quickly disintegrate into rival principalities.

He was the eldest son of Vladimir II Monomakh by Gytha of Wessex.^[3] He is figured prominently in the Norse Sagas under the name Harald, to allude to his grandfather, Harold II of England.

Mstislav was born in Turov. As his father's future successor, he reigned in Novgorod from 1088 to 1093 and (after a brief stint at Rostov) from 1095 to 1117. Thereafter, he was Monomakh's co-ruler in Belgorod Kievsky, and inherited the Kievan throne after his death. He built numerous churches in Novgorod, of which St. Nicholas Cathedral (1113),^[4] and the cathedral of St Anthony Cloister (1117) survive to the present day. Later, he would also erect important churches in Kiev, notably his family sepulchre at Berestovo and the church of the Assumption of the Mother of God in Podol.^[5]

Mstislav's life was spent in constant warfare with the Cumans (1093; 1107; 1111; 1129), Estonians (1111; 1113; 1116; 1130), Lithuanians (1131), and the princedom of Polotsk (1127; 1129). In 1096, he defeated his uncle Oleg of Chernigov on the Koloksha River, thereby laying foundation for the centuries of enmity between his and Oleg's descendants. Mstislav was the last ruler of the united state of Rus', and upon his death, as the chronicler put it, "the land of Rus was torn apart". He died in Kiev, aged 55.

After his death, the state began to quickly disintegrate.^[6] At the time of Monomakhs's death, there had been only two main groups in the princely family, the Monomakhovichi and Olgovichi, but as the family proliferated, it broke up into a number of local branches and sub-branches.^[7]

In 1095, Mstislav married Princess Christina Ingesdotter of Sweden, daughter of King Inge I of Sweden.^[8] They had many children:

1. Ingeborg of Kiev, married Canute Lavard of Jutland, and was mother to Valdemar I of Denmark
2. Malmfred, married (1) Sigurd I of Norway; (2) Eric II of Denmark
3. Eupraxia, married Alexius Comnenus, son of John II Comnenus
4. Vsevolod of Novgorod and Pskov
5. Maria Mstislavna of Kiev, married Vsevolod II of Kiev
6. Iziaslav II of Kiev
7. Rostislav of Kiev
8. Sviatopolk of Pskov
9. Rogneda, married Yaroslav of Volhynia
10. Xenia, married Briachislav of Izyaslavl

Christine died on January 18, 1122; later that year Mstislav married again, to Liubava Dmitrievna Zavidich, the daughter of Dmitry Saviditsch, a nobleman of Novgorod. Their children were:

1. Vladimir III Mstislavich (1132–1171)
2. Euphrosyne of Kiev, (c. 1130 – c. 1193) married King Géza II of Hungary in 1146.

Through Euphrosyne, Mstislav is an ancestor of both Philippa of Hainault and King Edward III of England, hence of all subsequent English and British monarchs. Through his mother Gytha, he is part of a link between Harold II of England and the modern line of English kings founded by William the Conqueror, who deposed him.