Gelada Baboon (Theropithecus gelada), Simien Mountains National Park, Ethiopia.

According to Wikkipedia:

The Gelada (Theropithecus gelada), sometimes called the Gelada Baboon, is a species of Old World monkey found only in the Ethiopian Highlands, with large populations in the Semien [sic] Mountains. Theropithecus is derived from the Greek root words for "beast-ape."

Like its close relatives the baboons, it is largely terrestrial, spending much of its time foraging in grasslands.

Since 1979 it has been customary to place the Gelada in its own particular genus (Theropithecus), though some genetic research suggests that this monkey should, in fact, be grouped with [baboons]; other researchers have classified this species even farther distant from [baboons].

Theropithecus gelada can be physically distinguished from baboons by the bright patch of skin on its chest. This patch is hourglass-shaped, and on males, bright red and surrounded by white hair. On females the patch is far less pronounced.

However, when in oestrus, the female's patch will brighten, and a "necklace" of fluid-filled blisters forms on the patch. This is thought to be analogous to the swollen buttocks common to most baboons experiencing oestrus. This modification likely came about due to the Gelada's unique mode of feeding - it spends most of its waking hours grazing from an upright sitting position, rump hidden beneath and so unavailable for display.

The male Gelada's tail is about as long as the body and densely tufted at the tip; it also has a long and flowing mantle and mane.

The Gelada lives in small harems consisting of one male, several females, and their offspring. These smaller bands often join together to feed, forming groups of upwards of 350 individual monkeys. At especially good feeding spots, groups in excess of 670 individuals have been observed.

The Gelada is exclusively herbivorous but is specialised as a grass-eater, consuming every part of the plant (but favoring one part over the others depending upon season), from green blades (in the wet season) to seeds to rhizomes (in the dry season) to stalks, flowers, and fruits. It has the most opposable thumb of any of the catarrhine primates (not including humans), allowing it to pick apart grasses with great dexterity to select the most nourishing meal. It is one of the only true grazing monkeys.