Busir or Busir Glavan was Khagan

Khagan

Khagan or qagan , alternatively spelled kagan, khaghan, qaghan, or chagan, is a title of imperial rank in the Mongolian and Turkic languages equal to the status of emperor and someone who rules a khaganate...

 of the Khazars

Khazars

The Khazars were semi-nomadic Turkic people who established one of the largest polities of medieval Eurasia, with the capital of Atil and territory comprising much of modern-day European Russia, western Kazakhstan, eastern Ukraine, Azerbaijan, large portions of the northern Caucasus , parts of...

 in the late 7th century and early 8th century CE.

In 704 Justinian II

Justinian II

Justinian II , surnamed the Rhinotmetos or Rhinotmetus , was the last Byzantine Emperor of the Heraclian Dynasty, reigning from 685 to 695 and again from 705 to 711...

, who had been exiled at Chersones for nine years, arrived at Busir's court. Busir, perhaps seeking to use him in his political maneuverings with the Byzantine Empire

Byzantine Empire

The Byzantine Empire was the Eastern Roman Empire during the periods of Late Antiquity and the Middle Ages, centred on the capital of Constantinople. Known simply as the Roman Empire or Romania to its inhabitants and neighbours, the Empire was the direct continuation of the Ancient Roman State...

, welcomed Justinian and gave him his sister in marriage (the woman's Khazarian

Khazar language

Khazar was the language spoken by the Khazars, a semi-nomadic Turkic people from Central Asia. It is also referred to as Khazarian, Khazaric, or Khazari. The language is extinct and written records are almost non-existent....

 name is unknown, but she took the baptismal name of Theodora

Theodora of Khazaria

Theodora of Khazaria was the second Empress consort of Justinian II of the Byzantine Empire.- Family :She was a sister of Busir, Khagan of Khazars. Their relation to other Khazar rulers such as Bihar, father of Tzitzak, is unknown.- Marriage :...

.) Busir provided the couple with funds and a house in Phanagoria.

However, the winds of realpolitik soon shifted, and the new emperor, Tiberius III, offered Busir a substantial bounty for his brother-in-law's head. Busir dispatched two agents, Balgitzin

Balgitzin

Balgitzin , in the account of Theophanes the Confessor, was the Khazar tudun of Phanagoria during the sojourn of Justinian II in that town. He was dispatched, along with Papatzys, by Busir Khagan to kill Justinian in 704, after Busir was bribed by Tiberius III...

 and Papatzys

Papatzys

Papatzys was, in the account of Theophanes the Confessor, the Khazar tudun of Kerch during the sojourn of Byzantine emperor Justinian II in Phanagoria. He was dispatched, along with Balgitzin, by Busir Khagan to kill Justinian in 704, after Busir was bribed by Tiberius III...

, to kill Justinian, but the latter was warned by his wife, who bribed the assassins' slaves to learn the nature of their mission. Turning the table on his would-be killers, Justinian murdered the pair after a banquet and fled Phanagoria by ship, seeking aid from Khan Terval of Bulgaria

Bulgaria

Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

, with whose help he retook Constantinople.

Busir now attempted to make peace with Justinian, sending Theodora to Constantinople. He later became involved with, possibly instigating, a revolt by Justinian's officers in the Crimea

Crimea

Crimea , or the Autonomous Republic of Crimea , is a sub-national unit, an autonomous republic, of Ukraine. It is located on the northern coast of the Black Sea, occupying a peninsula of the same name...

, which led ultimately to the crowning of Bardanes as emperor and the death of Justinian in 711.