onager, (Equus onager), species of Asian wild ass that ranges from northwest Iran to Turkmenistan. The onager is pale-coloured and has a short erect mane and fairly large ears. It stands 1.5 metres (4.5 feet) at the shoulder and weighs about 250 kg (550 pounds). The onager was domesticated in ancient times but has been replaced by the domestic horse and donkey. It now is found in limited numbers and may be approaching extinction. The name onager is sometimes used for the Asian wild ass (Equus hemionus).
The Persian onager (Equus onager) lives in a lower semidesert or desert environment. It is now extremely rare and is unlikely to survive outside northeastern Iran and the Badkhyz Reserve in Turkmenistan. A small population lives in the semidesert salt plains of the Kavir Protected Region in Iran.
The Indian wild ass is a closely related, probably identical, form that is sometimes distinguished as the race E. h. khur. A fairly small population occupies salt flats in the Rann of Kachchh in Gujarat state, a remnant of the thousands found there at the end of World War II.