Tong Yabghu Qaghan was khagan of the Western Turkic Khaganate from 618 to 628 AD. His name is usually translated as "Tiger Yabgu" in Old Turkic. Another interpretation of his name is "sufficiency" or "completeness". He was the brother of Sheguy, the previous khagan of the western Göktürks, and was a member of the Ashina clan. Tong Yabghu's reign is generally regarded as the zenith of the Western Göktürk Khaganate. His clan was syncretized Buddhist and native folk religion.
Reign
Tong Yabghu maintained close relations with the Tang Dynasty of China, and may have married into the Imperial family. The Chinese BuddhistpilgrimXuanzang visited the western Göktürk capital Suyab in modern Kyrgyzstan and left a description of the khagan. Scholars believe the khagan described by Xuanzang was Tong Yabghu. Gao and La Vaissière argue that the khagan Xuanzang met was his son Si Yabghu, rather than Tong Yabghu. Xuanzang described the khagan as follows:
The khan wore a green satin robe; his hair, which was ten feet long, was free. A band of white silk wound round his forehead and hung down behind. The ministers of the presence, numbering two hundred in number, all wearing embroidered robes, stood on his right and left. The rest of his military retinue clothed in fur, serge and fine wool, the spears and standards and bows in order, and the riders of camels and horses stretched far out of .
According to the Old Book of Tang, Tong Yabghu's reign was once considered as the golden age of Western Göktürk Khaganate:
Tong Yehu Kaghan is a man of bravery and astuteness. He is good at art of war. Thus he controlled Tiele tribes to the north, confronted Persia to the west, connected with Kasmira to the south. All countries are subjected to him. He controlled ten thousands of men with arrow and bow, establishing his power over the western region. He occupied the land of Wusun and moved his tent to Qianquan north of Tashkent. All of the princes of western region assumed the Turk office of Jielifa. Tong Yehu Kaghan also sent a Tutun to monitor them for imposition. The power of Western Turks had never reached such a state before".
Campaigns against Persia
Tong Yabghu's empire fought with the Sassanids of Iran. In the early 620's the khagan's nephew Böri Shad led a series of raids across the Caucasus Mountains into Persian territory. Many scholars have identified Tong Yabghu as the Ziebel mentioned in Byzantine sources as having campaigned with the Emperor Heraclius in the Caucasus against the Sassanid Persian Empire in 627–628. It has long been maintained by some scholars, including Chavannes, Uchida, Gao and Xue Zhongzeng that Tong Yabghu cannot be positively identified with Ziebel and may actually have died as early as 626. These scholars point to discrepancies in the dates between Byzantine and Chinese sources and argue that definitively conflating Ziebel with Tong Yabghu is an exaggeration of the extant evidence. The latest research on this topic proves that they were right: if Tong indeed died in 628, Ziebel is to be identified with Sipi khagan, Tong Yabghu's uncle, who murdered him and rose briefly to the throne. Sipi was by then pronounced Zibil and he was a small khagan in charge of the western part of Tong Yabghu's empire, exactly as Ziebel was according to the Byzantine sources. Ziebel is described as the brother of Tong in the Byzantine sources, and as his uncle in the Chinese sources, a discrepancy which long precluded the identification. However uncle and elder brother is the same word in ancient Turkish, äçi, and the Chinese sources could not render this double meaning with their very precise system of kinship names. stretched between the Caspian seashore and the Caucasus for forty kilometers; they are still in existence.
Governance
Tong Yabghu appointed governors or tuduns to manage the various tribes and people under his overlordship. In all likelihood Tong Yabghu's nephew Böri Shad, and son of Zibil/Ziebel was the commander of the Khazars, the westernmost of the tribes owing allegiance to the Western Göktürks; this branch of the family may have provided the Khazars with their first khagans in the mid seventh century.
Death
In ca. 630 he was murdered by Külüg Sibir, his uncle and a partisan of the Dulu faction. Following the death of Tong Yabghu, the might of the Western Göktürks largely collapsed. Although the khaganate lingered for a few decades before falling to the Chinese Empire, many of the client tribes became independent and a number of successor states, including the Khazar Khaganate and Great Bulgaria, became independent.
