This short paper deals with the title of the first ruler of the Western Turks. The brother of Bund'n qa gan, the founder of the Turkic Empire organised an independent centre in the West. The Orkhon Inscriptions call him Istämi qa gan. The Byzantine sources call him Siliziboulos or Silziboulos which is a Greek form of an Iranian Sirjibu g/Siljibu g. We have a western Turkic coin, the ruler on which is called sri iapgu saho. The form Silziboulos thus can be a form of an original sri yab gu ('Lord yab gu').
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