Gelada (Theropithecus gelada) is a species of Old World monkey, found only in the highlands of Ethiopia and Eritrea. Like baboons, they are terrestrial, and spend their time foraging in grasslands. Some authorities used to group the Gelada with baboons in the genus Papio, but since 1979 it has become customary to place them in a separate genus, Theropithecus. Theropithecus gelada is the only living species, but at least two separate lineages are known in the fossil record. While Geladas are restricted to Ethiopia and Eritrea today, fossils of the genus are known from South Africa, Malawi, Democratic Republic of the Congo, Tanzania, Uganda, Kenya, Ethiopia, Algeria, Morocco, Spain, and India.

Theropithecus gelada can be distinguished from baboons by the bright patch of skin on their chests. The patch is hourglass shaped, and on males, it is bright red and surrounded by white hair. On females, the patch is far less pronounced. However, when in heat, the female's patch will brighten, and a "necklace" of fluid-filled blisters forms on the patch. This is thought to be similar to the swelling on the buttocks during oestrus that is common to all baboons.

A female Gelada

Geladas live in small groups with one male, and several females and their offspring. These small bands often join together to feed, creating groups of upwards of 350 individual monkeys. At especially good feeding spots, group of upwards of 670 Geladas have been observed.

Geladas are primarily grass-eaters, eating every part of the plant, from the seeds, to the roots, to the stalk. They have the most well developed opposable thumbs of any of the Old World monkeys, which allows them to pick apart grasses with great dexterity to find the nourishing parts. They have also been known to eat fruit on occasion.

Although not listed as endangered, only 50-60,000 Geladas are known to exist. Hunting and habitat destruction have forced the Geladas into areas formerly inhabited by Olive Baboons, and hybridisation between the two groups has been observed. In addition, in the southern part of the Amhara plateau, Gelada males are killed every two years in order to use their manes in a coming-of-age ceremony. The loss of much of the adult male population on a regular basis has disrupted the population of the species.

There are two subspecies of Gelada:

• Theropithecus gelada gelada
• Theropithecus gelada obscurus