According to

John Skylitzes John Skylitzes, commonly Latinized as Ioannes Scylitzes (, ; , ; early 1040s – after 1101), was a Byzantine historian of the late 11th century. Life Very little is known about his life. The title of his work records him as a '' kouropalat ...

, Sfengus or Sphengos was a brother of

Vladimir I of Kiev Vladimir I Sviatoslavich or Volodymyr I Sviatoslavych (; Christian name: ''Basil''; 15 July 1015), given the epithet "the Great", was Prince of Novgorod from 970 and Grand Prince of Kiev from 978 until his death in 1015. The Eastern Orthodox ...

. Sfengus was a leader in the joint

Byzantine The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the events that caused the fall of the Western Roman E ...

- Kievan campaign to depose

Georgius Tzul Georgius Tzul (also ''Georgios''; ) was a Khazar warlord against whom the Byzantine Empire and Mstislav of Tmutarakan launched a joint expedition in 1016. He appears only in the account of the Byzantine court historians Kedrenos and John Skyl ...

, the last recorded

khagan Khagan or Qaghan (Middle Mongol:; or ''Khagan''; ) or zh, c=大汗, p=Dàhán; ''Khāqān'', alternatively spelled Kağan, Kagan, Khaghan, Kaghan, Khakan, Khakhan, Khaqan, Xagahn, Qaghan, Chagan, Қан, or Kha'an is a title of empire, im ...

of the

Khazars The Khazars ; 突厥可薩 ''Tūjué Kěsà'', () were a nomadic Turkic people who, in the late 6th century CE, established a major commercial empire covering the southeastern section of modern European Russia, southern Ukraine, Crimea, a ...

. Though identified as a brother of Vladimir I of Kiev, some historians such as Simon Franklin and

Jonathan Shepard Jonathan Shepard (born 1948) is a British historian specialising in early medieval Russia, the Caucasus, and the Byzantine Empire. He is regarded as a leading authority in Byzantine studies and on the Kievan Rus. He specialises in diplomatic and ...

hypothesize that he is identical with

Mstislav of Tmutarakan Mstislav Vladimirovich (died ) was the earliest attested prince of Tmutarakan and Principality of Chernigov, Chernigov in Kievan Rus'. He was a younger son of Vladimir I of Kiev, Vladimir the Great, the grand prince of Kiev. His father appointed ...

, Vladimir's son.

Sources

Franklin, Simon and Jonathan Shepard. ''The Emergence of Rus 750-1200''. Longman, 1996. Military history of the Khazars 11th-century princes from Kievan Rus' {{Russia-bio-stub