Chagatai Khan

Among the sons of Genghis Khan, Chagatai (1183-1242) earned a particular reputation as the guardian of his father's law. The second son of Genghis Khan and Börte, he was regarded within the family as the strictest upholder of the yasa, the body of Mongol legal custom attributed to the conqueror, and of traditional steppe usage generally; later Persian historians portray him as a ruler whom even fellow princes feared to cross in matters of law.

Chagatai fought in the major campaigns of his father's reign, including the war against the Jin dynasty and the conquest of the Khwarazmian Empire, where he shared command of the siege of Urgench with his brothers Jochi and Ögedei. His relations with Jochi were openly hostile; he questioned his elder brother's paternity, recalling Börte's captivity among the Merkits before Jochi's birth, and the quarrel was a factor in Genghis Khan's decision to pass over both of them and designate the third brother, Ögedei, as heir. Chagatai accepted the choice and remained a loyal supporter of Ögedei's election in 1229 and of his reign thereafter, serving as a senior voice in dynastic councils.

His own inheritance comprised the lands of the former Qara Khitai empire in Central Asia — Transoxiana, the Tarim basin, and the surrounding steppe — which became the Chagatai ulus, one of the four great divisions of the Chinggisid world alongside the Golden Horde of Jochi's descendants, the east Asian realm that became the Yuan dynasty, and the Persian territories later organized as the Ilkhanate by his great-nephew Hulagu. Chagatai governed the sedentary cities of his domain largely through appointed administrators, notably the merchant-official Mahmud Yalavach and his son Masud Beg, while the khan himself kept to the nomadic life of the steppe.

Chagatai died in 1242, shortly after Ögedei, leaving the khanate to a succession of descendants whose fortunes rose and fell with the empire's internal wars. The ulus that bore his name proved remarkably durable as a source of legitimacy. In the fourteenth century Timur, though not a Chinggisid himself, ruled the khanate's western half through puppet khans of Chagatai's line and married into the family, while the eastern portion persisted as Moghulistan. Through Babur, a descendant of Chagatai on his mother's side, the line's prestige passed even to the Mughal dynasty of India.