Bayan of the Mergid (died 1340) was a Mongol general of the Mergid clan and an official in the Yuan Dynasty. At the turn of the 13th/14th centuries he, together with the TurkEl Temür, was a member of the group around Qaishan, a nephew of Temür Khan who was appointed to defend Mongolia against the Chagatai Khanate under Kaidu, the grandson of Ögedei. In one battle, he repelled and chased the Ögedeid army; and was given the title of Baghatur. After Temür's death, Qaishan emerged as the new Yuan emperor, and Bayan was among those who received an official position as as reward. Later, Bayan was governour of Henan. Historians describe him as a traditionalist who attempted to preserve Mongolian culture while he is seen as a violent aristocrat by some.
In the conflicts about the succession of Tugh Temür Khan after 1332, Bayan broke with El Temür and supported Toghon Temür, who ascended the throne in 1333 (the same who would lose China in 1368). He was appointed commander of kheshig, composed of Mongols, Kypchaks, Russians and Asud in 1334. Until 1335 Bayan succeeded in annihilating El Temür's sons and family. Bayan began concentrating official positions in his person that had not been so concentrated before. He implemented rather conservative politics, abolishing the imperial examination system, and aimed to contain the number of Han Chinese in the upper echelons of the Yuan bureaucracy. He once suggested the emperor kill those Han Chinese of the more numerous surnames: Zhang, Wang, Liu, Li and Zhao to suppress the rebellion. In 1339 he became great chancellor (Chinese: 大丞相; pinyin: dà chéngxiàng). At that time he had probably gone too far, in any case he was toppled in 1340 by his nephew Toghtogha. Shortly after that, his purges were called off and his policies were reversed.