According to

John Skylitzes John Skylitzes, commonly Latinized as Ioannes, la, Johannes, label=none, la, Iōannēs, label=none Scylitzes ( el, Ἰωάννης Σκυλίτζης, ''Iōánnēs Skylítzēs'', or el, Σκυλίτση, ''Skylítsē'', label=none ; la, ...

, Sfengus or Sphengos was a brother of

Knyaz , or ( Old Church Slavonic: Кнѧзь) is a historical Slavic title, used both as a royal and noble title in different times of history and different ancient Slavic lands. It is usually translated into English as prince or duke, dependi ...

Vladimir I of Kiev Vladimir I Sviatoslavich or Volodymyr I Sviatoslavych ( orv, Володимѣръ Свѧтославичь, ''Volodiměrъ Svętoslavičь'';, ''Uladzimir'', russian: Владимир, ''Vladimir'', uk, Володимир, ''Volodymyr''. Se ...

. Sfengus was a leader in the joint

Byzantine The Byzantine Empire, also referred to as the Eastern Roman Empire or Byzantium, was the continuation of the Roman Empire primarily in its eastern provinces during Late Antiquity and the Middle Ages, when its capital city was Constantinopl ...

- Kievan campaign to depose Georgius Tzul, the last recorded

khagan Khagan or Qaghan (Mongolian:; or ''Khagan''; otk, 𐰴𐰍𐰣 ), or , tr, Kağan or ; ug, قاغان, Qaghan, Mongolian Script: ; or ; fa, خاقان ''Khāqān'', alternatively spelled Kağan, Kagan, Khaghan, Kaghan, Khakan, Khakhan ...

of the

Khazars The Khazars ; he, כּוּזָרִים, Kūzārīm; la, Gazari, or ; zh, 突厥曷薩 ; 突厥可薩 ''Tūjué Kěsà'', () were a semi-nomadic Turkic people that in the late 6th-century CE established a major commercial empire coverin ...

. Though identified as a brother of

, some historians such as Simon Franklin and Jonathan Shepard hypothesize that he is identical with

Mstislav of Tmutarakan Mstislav Vladimirovich (; ; ) was the earliest attested prince of Tmutarakan and Chernigov in Kievan Rus'. He was a younger son of Vladimir the Great, Grand Prince of Kiev. His father appointed him to rule Tmutarakan, an important fortress by t ...

, Vladimir's son.

Sources

Franklin, Simon and Jonathan Shepard. ''The Emergence of Rus 750-1200''. Longman, 1996. Khazar military history 11th-century princes in Kievan Rus' {{Russia-bio-stub