Diana monkeys belong to the Old World monkey family. They are generally black or dark grey but have a white throat, crescent-shaped browband, ruff, and beard. The browband gave the species its common name since it was held to resemble the crescent on the brow of the goddess Diana. These monkeys have white underarms and a white stripe down their thighs. The backs of their thighs and their lower backs are a chestnut color. Apart from the browband, ruff and beard, and some fringes on their limbs, their fur is short and sleek in appearance.
Diana monkeys are diurnal creatures. They are active during the day. They feeds at all levels of the canopy, and rarely come down to the ground. Diana monkeys sleep in the upper levels of the trees at night, though they do not make nests. They are social and live in groups that consist of a single male with a number of reproducing females and their infants. Diana monkeys are noisy forest dwellers. Their marked coloration allows a wide range of visual social signals for communication, and they also have a wide range of alarm calls, with different sounds for different predators. For example, Yellow-casqued hornbills are able to discriminate these sounds and take appropriate action.
Diana monkeys are polygynous. This means that males mate with more than one female during the breeding season. In good conditions, females reproduce annually. They give birth to a single infant. The gestation period lasts about 5 months, and the young nurse for a further 6 months. Although the young are born in a fairly well-developed condition, with open eyes and able to grasp their mothers, at least in zoo conditions, mothers rarely let young infants leave them. As infants grow, however, they become very playful. Juveniles reach reproductive maturity at an age of about 3 years. Daughters remain in their mothers' social groups, while males leave their natal groups shortly before becoming reproductively mature.
Main threats to Diana monkeys include habitat destruction and hunting for bushmeat. Deforestation due to logging, conversion to agricultural land and charcoal production, reduces the habitat of these monkeys. Diana monkeys is a preferred game species because of the value of their skin and meat.
The IUCN Red List and other sources don’t provide the number of the Diana monkey total population size. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List and its numbers today are decreasing.
Due to their frugivorous diet, Diana monkeys are likely to act as seed dispersers of their range. Additionally, they are prey items for some local predators.