Bayan was a warrior of the Buryat tribe serving as a commander for the Mongol Empire and its Great Khan, Möngke, during the 13th century. Following the death of the Khan, his son, Asutai, recruited Bayan both as a Keshig part of the Imperial Guard, and as a member of the Templar Order.
During Summer 1259, as Möngke Khan was on a campaign to conquer the Song Empire in China, Bayan was part of the army which besieged the Song forces entrenched in the Diaoyu Fortress. However, plagued by diseases and faced with the strong resistance of the Songs, the Mongols were unsuccessful in their attempts to break the fortress defences.
When his superior, the general Köke, asked for volunteers for a new assault, Bayan offered himself and his men to join the attack. Led by Möngke's commander-in-chief, Wang Dechen, the mongols attacked the wall using the cover of the night but somehow warned of their arrival the chinese ambushed them with archers and canons. During the battle, Bayan killed a deadly Chinese veteran, who unknow to the Mongol warrior was in fact a Assassin. After their retreat, Bayan brought back the seriously injured Wang Dechen to the Mongol camp, but the shaman's ritual failed to save him despite the command of Möngke.
Several days later, as the Mongols morale has fallen following the loss of Wang, Bayan had come to believe in a secret entrance to the fortress, which could explain how the Chinese were able to set an ambush outside of their walls without being seen. After requesting permission, Bayan left the camp to scout around the walls, looking for a hidden cave. During his nocturnal exploration, Bayan spotted what he believed to be a Song scout but failed to capture her, loosing her tracks. Unable to find the entrance, the Mongol warrior decided to hide and to wait for the return of the scout, planning to capture her and to extort from her the location of the hidden passage.
When the scout returned, Bayan shot an arrow in her leg from his hidding spot, hitting her knee as she was freerunning. Facing the crippled woman, who was in fact Zhang Zhi, an Assassin novice and the daughter of the veteran he killed several days before, Bayan had to retreat after Zhang shot him with a poisoned bolt and stabbed him with her Hidden Blade. Through sheer will and despite the poison taking his toll on him, the half-dead warrior dragged himself to the Mongol camp before falling unconscious.
When Bayan woke up he learned from Prince Asutai that the Great Khan had been murdered in his sleep by the Assassin girl before Bayan crippled her. Impressed by his skills, Asutai also revealed to Bayan that he planned to hide that his father was murdered by a Song and to told the men that the Khan died from the same disease plaguing his army. Asutai then promoted Bayan to the Keshigs, the Imperial Guards, and informed him that he would accompany him to Mongolia, where Möngke was to be buried alongside the other Great Khans.
One month later, on their way to Mongolia, Asutai revealed to Bayan the existence of the Templar Order and the fact that his late father, himself and most of the Keshigs were Templars. He then offered Bayan to join them and the Mongol accepted.
- Bayan is an ancestor of Natalya Aliyev, a 21th century teenagers working for the Templars.