Hulagu was born to Tolui, one of Genghis Khan's sons, and Sorghaghtani Beki, an influential Keraite princess. Sorghaghtani successfully navigated Mongol politics, arranging for all of her sons to become Mongol leaders. She was a Christian of the Church of the East (often referred to as "Nestorianism") and Hulagu was friendly to Christianity. Hulagu's favorite wife, Doquz Khatun, was also a Christian, as was his closest friend and general, Kitbuqa. It is recorded however that he converted to Buddhism as he neared death, against the will of Doquz Khatun. The erection of a Buddhist temple at Ḵoy testifies his interest in that religion.
Hulagu had at least three children: Abaqa Khan, Tekuder, and Taraqai. Abaqa was second Ilkhan of Iran from 1265–82, Teguder Ahmad was third Ilkhan from 1282–84, and Taraqai's son Baydu became Ilkhan in 1295. Mīr-Khvānd mentions two more children, given as Hyaxemet and Tandon in an early translation; Hyaxemet initially served as governor of Armenia and Azerbaijan, while Tandon was given Diyarbakır and Iraq. The order of birth is listed as Abaqa, Hyaxemet, Tandon, Teguder, then Taraqai. His daughter-in-law, Absh Khatun, was sent to Shiraz to reign in 1263.