either of two species belonging to the horse family, Equidae, especially the African wild ass, Equus asinus (also, Equus africanus), often referred to as the true ass. The related Asiatic wild ass, often called the half-ass (E. hemionus), is usually known by the local names of its various races: e.g., kulan (E. h. hemionus, Mongolia); kiang (E. h. kiang, Tibet); onager (E. h. onager, Iran and Turkmenistan); and ghorkhar (E. h. khur, India and Pakistan). The Syrian wild ass (E. h. hemippus) is probably extinct. The donkey is a domesticated descendant of E. asinus.

Asses are small, sturdy animals, ranging from 90 to 150 cm (3 to 5 feet) high at the shoulder. The African wild ass is bluish gray to fawn; the half-ass, lighter in colour, is reddish to yellow-gray. Both have whitish muzzles and underparts, short, dark, erect manes lacking a forelock, and tufted tails. Most asses have a dark stripe from the mane back onto the tail, but only the Nubian ass (E. a. africanus) regularly has a prominent stripe across the shoulders, as does the donkey. The half-ass differs from the true ass in its extremely long, slender legs, shorter ears (intermediate between those of the horse and donkey), and larger hooves. The bray of the half-ass lacks the alternating low tones heard in the “hee-haw” of the true ass. The ass is a swift runner: kulans have been clocked at 64.4 km/h (40 miles per hour). In ancient times half-asses, especially the onager, were tamed and trained for work. These lighter-bodied animals were eventually rejected in favour of the sturdier donkey.

Desert dwellers, wild asses often inhabit very arid regions that cannot support other large mammals. African wild asses are territorial, mature males (stallions) maintaining areas in which they are dominant over other asses. The only strong social bond is between the female and her foals, herds being formed only when individuals travel together casually. Kulans live in herds consisting of one stallion and several females with their young. These family groups join to form large herds during the winter season.