According to The I-Spyder Book of Earth Creatures, the mountain gorilla — formally known as Gorilla beringei beringei —was a shy herbivore that lived in forests. Its natural habitat was in the north-central African nations of Rwanda, Uganda and the Democratic Republic of Congo. Males were often twice the mass of females. When adult, males could be further distinguished from females by the presence of silver fur on their backs, leading to the secondary name, silverback.

Unlike humans, a mountain gorilla's arms were longer than its legs, which forced the animal to either adopt a four-limbed approach to walking or walk on two legs with its knuckles dragging.

The creatures were last seen on Earth in 2030, and had been killed off because their habitat was destroyed and they were hunted by humans for bushmeat. However, the last mountain gorilla was really sent to the Museum of the Last Ones, until it was sent back to its own time by the Tenth Doctor.

They had an I-Spyder point value of 500. (PROSE: The Last Dodo)