When Mongols moved into the appanage of chagatai in the thirteenth century, the area was occupied by Turkic-speaking peoples. The ancestors of the Hazara Mongols appear to have been influenced by their Turkic subjects during their stay in Transoxiana, for many Turkic as well as Mongol words are present in modern Hazara speech. In Afghanistan the ancestral Hazaras became Persian-speaking. At the beginning of the sixteenth century some Hazaras still spoke Mongol, by the twentieth century, Mongol survived only as a minor vocabulary element. Bellew characterized the Hazara language as representing a thirteenth-century form of Persian. Morgenstierne, a trained linguist, more cautiously described Hazara speech as "a peculiar dialect of Persian". No descriptive study has been made of any of the Hazaras as are literate.
At some period after their entry into Afghanistan the ancestors of the Hazara Mongols adopted the Shi'a Muslim "twelver" faith of the Persians. All Hazaras dwelling within the Hazarajat are "twelvers". Such Hazaras on the periphery of the Hazarajat as have been converted to other Shia sects or to the Sunni Muslim religion are not regarded by the twelvers as being properly Hazaras.