Chagatai Khan: Son of the Genghis Khan and Börte

Genghis Khan and Börte had a son named Chagatai Khan. Following his father's death, he inherited the majority of what are now five Central Asian states. Genghis Khan also appointed him to supervise the enforcement of the Yassa, Genghis Khan's codified code of law.

Chagatai's early life is shrouded in mystery. He was Genghis Khan's and Börte's second son. Because he refused to acknowledge Jochi as a full-brother, Chagatai was regarded as hot-headed and temperamental by his relatives. Among his relatives, he was the most outspoken on the subject. In 1206 his father awarded him four mingghans commanded by Qarachar of Müge, Barlas, Kököchü of Baarin, of Jalairs, and Idiqudai Noyan, as well as an appanage around the Altai Mountains. He accompanied Jochi and Ögedei in an invasion of the Jin Empire in 1211, seizing several cities and entering Shaanxi and Henan in 1213, sacking Yanggu. Later, Chagatai joined his father and brothers in a battle against the Khwarazmian Empire, taking Otrar in 1218, Samarkand in 1220, and Urgench in March-April 1221. Because Chagatai and Jochi refused to cooperate, the Urgench campaign was substantially more difficult. Following this episode, Gedei was named commander of the besieging forces, while Chagatai was tasked with maintaining contact with Mongol armies by repairing roads and erecting bridges. During his siege of Talaqan, he returned to his father's side. When Chagatai's son Mutukan was murdered during the siege of Bamiyan in 1221, he was devastated. He was there at the fight at the Indus River where Jalal ad-Din Mingburnu was defeated. Later, during the invasion of Western Xia, he led the rear guard.

Chagatai prospered Genghis Khan in his domains in what became recognized as Chagatai Khanate in 1227 through its capital in Almaliq city, in the vale of the Greater Ili, nearby the site of the present Kulja, and accordingly in the extreme east of his dominion. He was present at Ögedei's enthronement ceremony on 13 September 1229 as the eldest surviving son and head of the family, and he supported his reign. Güyük was sent as Chagatai's ward by Ögedei. Although Rashidaddin said that Chagatai died shortly before Ögedei, Juvayni reported on Chagatai's subsequent activities, including his strong support for Töregene's regency. He died, though, not long after.

Vajir, Baha al-Din Marghinani, and Habash Amid are some of his recognized viziers. Various authors have described Vajir as Turkish, Uyghur, and Khitan. Qushuq Noyan of the Jalayir tribe hired him to work in the court of Chagatai. Chagatai valued him highly since he had produced a book about the Mongol Empire's history. He even permitted him to put one of his daughters-in-law to death for adultery. Vajir was hanged for treason alongside Chagatai's physician Majd al-Din after Chagatai's widow Yesülün accused them of poisoning Chagatai. Habash Amid was initially a secretary and a Muslim Khwarazmian from Otrar. He was dispatched to Chagatai in 1218, and thanks to his backing for Qara Hülegü, he survived the purge. Baha al-Din Marghinani, a companion of Yesü Möngke's son, also survived Chagatai, but he was later purged.

Chagatai had several wives and concubines in addition to his two main spouses.

Table: List of principal wives along with other wives and concubines

Table: List of children by concubines

He was a just and competent ruler, according to Rashidaddin. He was also regarded as noble and open-hearted by Minhaj-i-Siraj Juzjani. On the other hand, Muslims regarded Chagatai Khan with suspicion and hostility because he zealously enforced Mongol Yasa law, which prohibited Halal animal slaughter and Islamic prayer ritual washing, as well as the Islamic legal system. In addition, he is responsible for the Chagatai language, as well as persons with the surname Chughtai, the Iranian city of Joghatai, and the Azerbaijani village of Ciğatay.