Research on historical change of Tatar people is necessary for understanding history of Eastern Mongolia region from Baikal through Manchu area. This research tries to study Tatar, as historical term, who were appeared in Mongol plateau and Northeast Asia from A.D. 8th through 13th century, not the people called Tatar in present. With that, the true nature of Daldan (??) people, appeared in East Asian history from the period of Ming (明) China, is reviewed. As the result, first written name of Tatar in Chinese character was found as Shiwei (室韋), and its original name was Tatar. Moreover, Tatar people at the period of Tang China can be divided into Toquz Tatar (Tatar with nine family names) around Baikal region and Otuz Tatar (Tatar with thirty family names) around Ergune River and Nun River. Otuz Tatar can be noted because they formed a part of Korean ancient history. Damo Shiwei (達末室韋) as a part of Otuz Tatar at the period of Tang Dynasty was formed with Dumakru (豆莫婁) or Dalmalru (達末婁) people who were descendants of Northern Buyeo (北夫餘). Dumakru is determined as the people who led Baijinbao-Hanshu (白金寶-漢書) Culture according to Chinese Archeologists.