The Onager (Equus hemionus) is a large member of the genus Equus of the family Equidae (horse family) native to the deserts of Syria, Iran, Pakistan, India, Israel, and Tibet. It is sometimes known as the Wild Asian Ass.
Like many other large grazing animals, its range has contracted greatly under the pressures of hunting and habitat loss, and of the six subspecies, one is extinct and two endangered. The Kiang (E. kiang), a Tibetan relative, was previously considered to be a subspecies of the Onager as E. hemionus kiang, but recent molecular studies indicate that it is a distinct species.
The specific name is Ancient Greek ἡμίονος (hēmíonos), from ἡμι- (hēmi-), half, and ὄνος (ónos), donkey; thus, half-donkey or mule. In Persian the archaic word, "gur" preserves the second syllable of the common Indo-European term that include ona/ono (donkey) and ger/gur, (swift)
Onagers are a little larger than donkeys at about 290 kilograms (640 lb) and 2.1 metres (6.9 ft) (head-body length), and are a little more horse-like. They are short-legged compared to horses, and their coloring varies depending on the season. They are generally reddish-brown in color during the summer, becoming yellowish-brown in the winter months. They have a black stripe bordered in white that extends down the middle of the back. They are notoriously untameable. Equids were used in ancient Sumer to pull wagons circa 2600 BC, and then chariots on the Standard of Ur, circa 2000 BC. Clutton-Brock suggested that these were donkeys rather than onagers on the basis of a "shoulder stripe" (1992:88). However, close examination of the animals (equids, sheep, and cattle) on both sides of the piece indicate that what appears to be a stripe may well be harness, trapping, or a joint in the inlay. For Sumerian references to onagers, see Heimpel (1968) and Maekawa (1979).