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 (where it was reintroduced between 1982-1987), Central Asia, and Mongolia. 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. It is also known as the Asiatic wild ass,Asian wild ass, or wild Asian ass (in which case the term "onager" is reserved for the E. h. onager subspecies, more specifically known as the Persian onager).
Like many other large grazing animals, the onager's range has contracted greatly under the pressures of poaching and habitat loss. Of the five subspecies, one is extinct and at least two are endangered (their status in China is not well known).
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 includes 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.
Onagers are notoriously untamable. Equids were used in ancient Sumer to pull wagons circa 2600 BC, and then chariots on the Standard of Ur, circa 2550 BC. Clutton-Brock (1992) suggests that these were donkeys rather than onagers on the basis of a "shoulder stripe". 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 a harness, a trapping, or a joint in the inlay.