Iduq qut Gaochang king, one of the Qocho Uyghur descendants leaving the 《Epitaph of Iduq qut Gaochang King》 in the 14th century, is the descendant of Bugu Jun(僕固俊) that set up the government, so-called Qocho Uyghur, in Turfan after 866. Even under the ruling of Mongolian Empire in the 14th century, he want to succeeded to Qocho Uyghur`s tradition. Bugu(僕固) tribe that he belonged to was one of the Turkish tribes that led a nomadic life in the past Mongolia. They not only grew during the ruling of Tang after the collapse of the Empire of Turks in the middle of 7th century, but were one of the powerful parties also in the period of Uyghur`s nomadic khaghanate(745~840). And they have long-lasting history setting up the government only after the mid-9th century and maintaining it for over 300 years. Iduq qut Gaochang king remembered and wrote down this past historical experience as name of the myth of ``Bogu qaghan``, the progenitor. This memory of his was not only related with Uyghur lived in the Mongolia that had close ties with himself among the historical issues that the past Turks made, but was associated with the effort to connect the legitimacy of Turkish nomads started from Gaocha (高車) in the 5th century with himself. Therefore, in order to systematize his own historical consciousness, Iduq qut Gaochang king completed the myth about ``Bogu qaghan`` mobilizing and synthesizing various motives. In that place, first, he emphasized the Tuul River of Mongolian steppe related to the mainland of Bugu tribe, and also borrowed the faith of a divine mountain(聖山) along with the joint of the two rivers(兩河). And he put emphasis on the divinity of the progenitor through the combination of divine trees(神樹) and sunlight(日光) that may have been related with the ultimate religious system of the steppe as well as the doctrine of Manichaeism. Moreover, explaining the existence of five sons from divine trees(木生五子) and his youngest sibling, Bogu qaghan, he tried to show their ties as a party in the past. This process was meant to identify the past traditions by combining the mythological motives of the steppe in northern Asia including the past Turks. And at the same time, it was also the process to justify the Bugu tribe that transmitted the legitimacy in the history. Therefore, Iduq qut Gaochang king could make the tradition of ``Uyghur`` of his own through the arrangement of the progenitor`s myth, and later, this created another historical substance of ``Uyghur``.