Khalga and Kaban were two Khazar 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...

s listed in the Cäğfär Taríxı

Cägfär Taríxi

The Cäğfär Taríxı is a controversial Russian language text purporting to be a partial translation of a 17th century Volga Bulgar compilation of early historical material on the Bulgars,...

, a Tatar language

Tatar language

The Tatar language , or more specifically Kazan Tatar, is a Turkic language spoken by the Tatars of historical Kazan Khanate, including modern Tatarstan and Bashkiria...

 book purporting to be a history of the early Turkic peoples

Turkic peoples

The Turkic peoples are peoples residing in northern, central and western Asia, southern Siberia and northwestern China and parts of eastern Europe. They speak languages belonging to the Turkic language family. They share, to varying degrees, certain cultural traits and historical backgrounds...

. According to that work they ruled during the 660s. They are not mentioned in any other historical source, and since Cäğfär Taríxı is believed to be a forgery created by the NKVD

NKVD

The People's Commissariat for Internal Affairs was the public and secret police organization of the Soviet Union that directly executed the rule of power of the Soviets, including political repression, during the era of Joseph Stalin....

, the existence of these two kings is highly suspect.