The Naimans 乃蠻, in Chinese sources also called Naima 乃馬, Naiman 乃滿, 廼蠻, 奈曼, 奈蠻, or 耐滿, were a people of pastoral nomads that lived in the western parts of the Mongolian plateau. They spoke a Türkic language anbd originally lived in the region later inhabited by the Qirqizes 黠戛斯. It is even probable that they were ethnically related to the latter. Sources of the Liao empire 遼 (907-1125) call them Nianbage 粘八葛, that of the Jin empire 金 (1115-1234) Nianba'en 粘拔恩.
In 1097 a leader of the Naiman, Tugusa 禿骨撒, presented tributes to the Liao court, in unison with the leader of the Mongolian 蒙古 tribes of the Zubu 阻卜 and the Merkits 蔑兒乞. When the Liao empire disintegrated under the attacks or the Jurchens 女真, founders of the Jin empire, Prince Yelü Dashi 耶律大石 and his household moved to the west and founded the Western Liao dynasty 西遼 (1124-1211). The Naimans became vassals of the Western Liao, but in 1175 the Naiman chieftain Saliya Intesi 撒里雅寅特斯, and the leader of the Kangli 康里 people (see Kangju 康居), Bogu 勃古, offered the Jin court to change sides and to become vassals of the Jurchens.
The Persian history Jami' at-tawārīkh (in Chinese called Shiji 史集) says that a considerable part of the Naimans consisted of members of a tribe or people called Bietieqi 別帖乞. This people was originally much stronger than the Naimans and the Kereyids 克烈 and was only later forced by the Naimans to become part of their federation. The Naimans were in the 12th century the most powerful nomad people in the area west of the Altai Range. Their eastern neighbours were the Kereyids, the Uyghurs 畏兀兒 lived in the south, the Kangli in the west, and the Kirgizes in the north.
The earliest mentioned leaders of the Naimans were Narheishi Taiyang 納兒黑失太陽 and his younger brother Yinanchi Khan 亦難赤汗 (also called Yinanchi Bilge Bugu Khan 亦難赤必樂格卜古汗). The latter once supported Wanghan's 王罕 younger brother Yelikehala 也力可哈剌 in the fratricidal strife for the power over the Kereyid. After Yinanchi's death his son was unable to hold the position of khan, but the second son Baibuhua 拜不花 revived the position of khan. His oldest son Buyulu Khan 不欲魯汗 decided to split off his tribe from the Naiman federation and moved to Mt. Heixin 黑辛八石 where he ruled as khan of the Naiman of Guchugudang 古出古愓乃蠻. The khans of the Naiman bore the title of taiyang 太陽 (tayang), which might be derived from the Chinese word dawang 大王 "great prince". The names Bügü 卜古 and Buyiruq 不欲魯 are clearly of Türkic origin and demonstrate that the Naiman were cultural heirs of the Türkish 突厥 and the Uyghur empires. The organisation and administration of the Naiman khan's court likewise followed the precedents of the earlier Türkish state, just like the tax and monetary systems, and the use of the Syriac script. Even in the question of religion, the Naimans continued the belief of the Türks in the Nestorian branch of Christianism, although the practice of shamanism continued to play an important role amont the Naimans.
The Naimans, although divided into two groups, continued being a powerful federation until the beginning of the 13th century. In 1203 Činggis Qaɣan, the Mongol leader, destroyed the Kereyids and incorporated them into the Mongol federation. Threatened by this new power, the khan of the Naimans united the remaining forces of the Kereyids and challenged Činggis Qaɣan in the battle of Mt. Hanghai 杭海山. The Taiyang Khan died after a heavy defeat at Mt. Nahu 納忽山, and Činggis Qaɣan prepared for a final attack on the remaining Naimans. Taiyang Khan's son Quchulü 屈出律 fled to the territory of Buyulu Khan. In 1206 the Mongols defeated the troops of the Naimans and Merkits.
Quchulü fled to the Western Liao court. Yelü Zhilugu 耶律直魯古 (Christian name Georgos, the Last Ruler 西遼末主, r. 1177-1211) welcomed him and gave him his daughter in marriage. Quchulü thereupon discarded Nestorianism and became a believer of Buddhism. He traveled around in the Liao empire and assembled the remaining forces of the Naiman that had likewise fled to the west and had sought refuge in Yemili 葉密立, Haiyali 海押立 or Beš Baliq 別失八里. Endowed with this force he even dared rebelling against emperor Zhilugu, arrested him and forced him to retire. Quchulü, whose Christian name was David, killed the local chieftain of Almaliq 阿力麻里 (modern Huocheng 霍城, Xinjiang) and forced the Muslim population of the Western Liao empire to become either Christians or Buddhists.
In 1218 Činggis Qaɣan ordered gneral Zhebie 哲別 to conquer the Western Liao empire. Emperor David fled to Sariq-köl in Badakhshan but was soon captured by the Mongols. The Naiman people were enslaved and given to the Mongol princes as a human booty. Part of them fled to China, where they became troops in Wanyan Chen's 完顔陳和尚 army that defended the cities of the Jin empire against the Mongols. One tribe of the Naimans, the Dalu 答魯乃蠻, were even allowed to occupy important official positions in the Mongol empire.