Bayan of the Ba'arin tribe is one of the most meritorious retainers of the Yuan, the Qa'an Ulus of the Mongol Empire. He was the key figure that subdued the Southern Song and united China after three hundred years of fragmented period. Therefore, it is natural that the Chinese official historical source Yuanshi, History of the Yuan has a large amount of records on him in it. However, we are not well informed of his early career. He was an envoy from the Hülegü Ulus to Qubilai's court, which is not widely known to modern researchers. We do not know what his status was in Hülegü's court and why he was dispatched to Qubilai. Moreover, we even do not know what his father's name was and how he died because the Chinese sources and the Persian sources have different records in them.
Therefore, this thesis surveys the early career and family of Bayan by examining sources of different authors and languages in order to bring the puzzles together to shed more light on the subject. Especially this thesis introduces Tibetan records on Bayan, which is rather new to the scholars who are interested in this one-hundred-eyed Mongol general. This multi-lingual research on Bayan would be an obvious example of the study of the history of the Mongol Empire.