The Jalayirs or Chajala (Chinese Chazhala 茶札剌, also called Chazhila 茶只剌, Zhazhila 扎只剌 or 劄只剌, Chachila 茶赤剌, Zhachila 札赤剌, Zhadalan 札答蘭, Chazhilai 插支來, 插只來, Yalayi'er 押剌亦而, Zhalayir 劄刺亦兒 or 札刺亦儿), were a Mongolian-speaking people of the Nilun 尼倫 federation. They saw themselves as descendants of the Boduancha'r 孛端察兒 family and therefore as relatives to the Borzhijin 孛兒只斤 family, to which Čingghis Qan belonged. They can therefore be called part of the tribal federation of the Tatars 韃靼. The term Jalayir is derived from the Turkic tribe name Yaglakar of the Uyghurs 回紇. Central Asian sources like the Jami' at-tawārīkh (Chinese name Shiji 史集) list some tribes of the Jalayirs that were called Zheti, Tuohulawen and Tuolongjir (Chinese renderings). They lived in the region of the Rivers Onon and Kerulen.
The people of the Jalayirs is first mentioned in the history Liaoshi 遼史, where it is said that the Jalayirs delivered tributes to the court of the Liao dynasty 遼 (907-1125). The Khitans 契丹 who had founded the Liao empire, called all steppe tribes Zubu 阻卜 and referred to the Jalayirs as the Zubu Zhaala 阻卜札剌. The Jalayirs often rebelled against their exploitations by the Khitans, so that the latter founded a military commission (jiedushi si 節度使司) to have a better control over the steppe people.
The Jalayirs had also conflicts with Qaidu Khan 海都汗, leader of the Tatars and ancestor of Chinggis Khan. The Jalayirs were later controlled by a leadar called Muqali 木華黎. In 1122, when the Jurchens 女真 conquered the Liao empire, the Jalayirs participated in Prince Yelü Dashi's 耶律大石 migration to the west, where he founded the Western Liao empire 西遼 (1124-1218). At the end of the 12th century the khan of the Jalayirs was called Zhamuhe 札木合. Zhamuhe supported Temüjin, the eventual Čingghis Qan, in his campaign against the Merkits 蔑兒乞. When the power of Temüjin grew, Zhamuhe decided to challenge him, but he lost the famous battle at Dalanbanzhusi 答闌版朱思 at the River Kerulen and his army dissolved.
In 1201 the Jalayirs allied with the Qonggirads 弘吉剌, the Sanzhiwu 散只兀 and the Hedajin 合答斤 and attacked Genghis Khan in the battle at River Hailar 海剌兒, but the allies lost. The Jalayirs thereafter lost their coherence and their families submitted to Genghis Khan. During the Yuan period 元 (1279-1368) many Jalayir leaders became generals of the Yuan armies. Part of the Jalayirs under Zhamuhe joined the Kereyids 克烈 and Naimans 乃蠻. In 1204 Čingghis Qan defeated these peoples and integrated them into the Mongolian federation. Those of the Jalayirs that had migrated to the west later merged with the local population of Uyghur, Kazakh and Uzbek origin.