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 Constantin ...

Kievan Kyiv, also spelled Kiev, is the capital and most populous city of Ukraine. It is in north-central Ukraine along the Dnieper River. As of 1 January 2021, its population was 2,962,180, making Kyiv the seventh-most populous city in Europe. Kyi ...

campaign to depose

Georgius Tzul Georgius Tzul (also ''Georgios''; el, Γεώργιος Τζούλης) 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 cou ...

, 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 Jonathan Shepard 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 archaeologic ...

hypothesize that he is identical with Mstislav of Tmutarakan, 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