Zachariah was a 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...

, reported in the account of St. Cyril

Saints Cyril and Methodius

Saints Cyril and Methodius were two Byzantine Greek brothers born in Thessaloniki in the 9th century. They became missionaries of Christianity among the Slavic peoples of Bulgaria, Great Moravia and Pannonia. Through their work they influenced the cultural development of all Slavs, for which they...

. The dates of his reign are unknown but he was khagan during Cyril's visit to Khazaria in 861. Although Cyril does not expressly state so, the fact that he had a Hebrew name suggests that the Khazars had already converted to Judaism

Judaism

Judaism ) is the "religion, philosophy, and way of life" of the Jewish people...

by the time of Cyril's visit.