The single species G. gorilla stands 1.25 to 1.75 meters on two feet. Actual height is a bit more, as G. gorilla stands with the legs slightly bent at the knees. There is no tail. The armspan exceeds standing height measuring between 2 and 2.75 meters. The chest can be up to 508 mm across with a circumference for adult males between 1.25 and 1.75 meters. Weights for adult females range from 70-140 kg. and 135-275 kg. for adult males. G. gorilla has bare face, ears, hands, and feet, as well as the chest of old males. There are color variations between subspecies: G. g beringei and G. g graueri both have black skin and hair, adult males developing a silvery saddle across the back between the shoulders and rump. G. g beringie can be distinguished by its longer, silkier fur, especially on the arms. G. g gorilla is more brownish or grayish and the male’s silvery saddle extends to the thighs and blends into the body color more.

The Western Gorilla's body is extremely stocky, the head is pointed at the crown and the eyes and ears are small. The muzzle is short with large nostrils. The forearm is much longer than the upper arm, and the hands are very large with thumbs that are larger than the fingers.

Preferred habitat is lowland tropical forest, but there are populations found in montane rainforest between 1,500 and 3,500 meters and in bamboo forests from about 2,500 to 3,000 meters. G. gorilla is primarily terrestrial but is very capable of climbing trees. Walking is done mostly on all fours, and bipedal locomotion has not been observed at distances greater than 18 meters. They do not swim and are even reluctant to wade across shallow water. This fact may play a role in the distribution of the species. G. gorilla nests are built mostly on the ground, but in areas where building materials are scarce, they are built in trees. All nests are used only for one night. Movements of a particular group appear to vary depending on the availability of food. During the wet season, groups average a distance of 596 meters per day and in the dry season an average of 1,240 meters per day. In the wild, G. gorilla is almost entirely vegetarian, consuming leaves, shoots, stems, small amounts of wood, roots, flowers, fruits, and sometimes grubs and small amounts of insects along with the plant material. In Gabon, G. gorilla has been frequently observed breaking into termite nests to feed on the insects.

Social groups usually consist of 1 silverback or adult male, 1 blackback, 3 adult females and 2 or 3 young. These subgroups are generally part of a larger troop with a range of 2 to 30 individuals, and an average of 17. Hierarchy is established by size and dominant male Gorillas lead their groups for years. The other adult male Gorillas are usually the offspring of the dominant male and are poised to inherit the leadership of their group. If there are other males within the group, they usually leave to live alone or to begin their own group. Unlike most other primates, females leave their parental group when they reach sexual maturity, joining another group or a lone male almost immediately.

Breeding does not occur during any particular season in the wild. Estrous cycles last about 27 days and estrus 1-3 days. Birth intervals are 3.5-4.5 year, unless the infant dies. Gestation estimates are 251-295 days and usually one offspring is produced, though twins do occur rarely. At birth, infants weigh about 2 kg. Sexual maturity is reached at age 8 in females and 10 in males, though breeding does not usually begin until ages 10 and 15 respectively.

G. gorilla is classified as endangered by the USDI and is on appendix 1 of the CITES.

G. gorilla is found in SE Nigeria, Cameroon, Rio Muni (Equatorial Guinea), Republic of Congo, SW Central African Republic, and Gabon.