It seems that the Hephtalites were an agricultural people with a developed set of laws. They were first mentioned by the Chinese, who described them as living in Dzungaria around AD 125. They displaced the Scythians and conquered Sogdiana and Khorasan before 425. After that, they crossed the Syr Darya (Jaxartes) River and invaded Persia. In Persia, they were initially held off by Bahram Gur but later around AD 483–85, they succeeded in making Persia a tributary state. After a series of wars in the period around AD 503-513, they were driven out of Persia and were completely defeated in AD 557 by Khosru I though their polity came under the Gokturks thereafter. The White Huns also invaded the regions of Afghanistan and Pakistan and succeeded in at one time, even extended their domain to include the Ganges valley. They temporarily overthrew the Gupta empire but were eventually driven out of India in 528 by a Hindu coalition and had to settle down in what is now Pakistan and Afghanistan.
For many years, scholars suggested that they were possibly of Tibetan or Turkic-stock, and it seems likely that at least some groups amongst the Hephthalites were Turkic-speakers. In 1959, Kazuo Enoki put forward the hypothesis that they were probably East Indo-Iranians as some sources indicated that they were originally from Tokharestan, which is known to have been inhabited by Indo-Iranian people in antiquity. Richard Frye is cautiously accepting of Enoki's hypothesis, whilst at the same time stressing that the Hephthalites "were probably a mixed horde". More recently Xavier Tremblay's very detailed examination of surviving Hephthalite personal names has indicated that Enoki's hypothesis that they were East Iranian may well be correct, but the matter remains unresolved in academic circles.
According to the Encyclopaedia Iranica and Encyclopaedia of Islam, Hephthalites possibly originated in northeastern Iran and northwestern India. They apparently had no connection with the European Huns, but may have been causally related with their movement. It is noteworthy that the tribes in question deliberately called themselves "Huns" in order to frighten their enemies.
The earliest information about the Ephthalites comes from the Chinese chronicles, in which it is stated that they were originally a tribe of the great Yue-Chi, living to the north of the Great Wall, and subject to the Jwen-Jwen (Rouran), as were also the Turks at one time. Their original name was Hoa or Hoa-tun; subsequently they styled themselves Ye-tha-i-li-to (厌带夷栗陁) after the name of their royal family, or more briefly Ye-tha (嚈噠) descended from one of the 5 Yuezhi families (which included Kushan). There were various theories about their origins documented by the ancient Chinese chroniclers, as well as by Procopius of Caesarea:
Procopius claims that the Hephthalites lived in a prosperous territory and that they were the only Huns with fair complexions. According to him, they did not live as nomads, acknowledged a single king, observed a well-regulated constitution, and behaved justly towards neighboring states. He also describes the burial of their nobles in tumuli, accompanied by the boon-companions who had been their retainers in their lifetimes; this practice contrasts with evidence of cremation among the Chionites in Ammianus and with remains found by excavators for the European Huns and remains in some deposits ascribed to the Chionites in Central Asia. It is therefore assumed that the Hephthalites constituted a second Hunnish wave who entered Bactria early in the fifth century AD, and who seem to have driven the Kidarites into Gandhara.
Some Hephthalites may have been a prominent tribe or clan of the Chionites. According to Richard Nelson Frye:
Just as later nomadic empires were confederations of many peoples, we may tentatively propose that the ruling groups of these invaders were, or at least included, Turkic-speaking tribesman from the east and north, although most probably the bulk of the people in the confederation of Chionites and then Hephtalites spoke an Iranian language and this was the last time in the history of Central Asia that Iranian-speaking nomads played any role; hereafter all nomads would speak Turkic languages.
The newly-discovered ancient writings found in Afghanistan reveal that the Middle Iranian Bactrian language written in Greek script was not the native idiom of the Hephthalites but the traditional language of administration in this region from Kushan times. There is also evidence of the use of a Turkic language under the Hephthalites. The Bactrian documents also attest several Turkic royal titles (such as Khaqan), indicating an important influence of Turkic people on the Hephthalites, although these could also be explained by later Turkic infiltration south of the Oxus.
The modern Chinese variation Yanda has been given various Latinised renderings such as "Yeda", although the more archaic Korean pronunciation "Yeoptal" 엽달 is more compatible with the Greek Hephthal and is certainly a more archaic form.
The term Haital means "big" or "powerful" in the dialect of Bukhara, but might also mean "seven".
Different spellings include Ephthalite, Epthalite, Ephtalite, Eptalite, Euthalite, Hepthalite, Hephtalite, and Heptalite.
According to Xavier Tremblay, one of the Heptalite ruler's name "Khingila" has the same root as the Sogdian xnγr and Wakhi xiŋgār and its meaning is "Sword". Toramāna is derived from Tarua-manah. The name Mihirakula is derived from Miθra-kula which is Iranian for Relier upon Mithra. In Sanskrit, Mihirakula would mean from the "Kul (family) of Mihir (Mithra)".
According to Janos Harmatta, the name Mihirakula is Iranian for "Mithra's Begotten".
In India, the Hephthalites were not distinguished from their immediate predecessors and are known by the same name Huna. The Huna had already established themselves in Afghanistan and the North-West Frontier Province of present day Pakistan by the first half of the fifth century, and the Gupta emperor Skandagupta had repelled a Hūna invasion in 455 before the Hephthal clan came along.
The Hephthalites with their capital at Bamiyan continued the pressure on South Asia's northwest frontier and broke east by the end of the fifth century, hastening the disintegration of the Gupta Empire. They made their capital at the city of Sakala, modern Sialkot under their Emperor Mihirakula.
After the sixth century, little is recorded in South Asia about the Hephthalites, and what happened to them is unclear; some historians surmise that the remaining Hephthalites were assimilated into the population of northwest India and Pakistan.
Eric Flint's Belisarius series makes frequent reference to Ye Tai warriors.