Tong Yabghu Qaghan

The rest of his military retinue [was] 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 [sight].

Many scholars have identified Tong Yabghu as the Ziebel[dubious – discuss] mentioned in Byzantine sources as having (as khagan of the Khazars) campaigned with the Emperor Heraclius in the Caucasus against the Sassanid Persian Empire in 627–628.

[17] It has long been maintained by some scholars, including Chavannes, Uchida, Gao and Xue Zhongzeng that Tong Yabghu cannot be positively identified with Ziebel (or any Khazar ruler) 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.

[19] 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.

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.

[21] Tong Yaghbu also supported the spread of Buddhism within his realm and patronised scholars from the monastery of Nalanda in India including the translator and monk, Prabhakāramitra.