Which great ape is found only on the island of Borneo?

The great ape found only on the island of Borneo is the Bornean orangutan.

The Bornean orangutan (Pongo pygmaeus) is an orangutan species endemic to Borneo, where it lives in lowland and montane rainforests. Its range includes the Malaysian states of Sabah and Sarawak and several Indonesian provinces on the island. It is the largest of the three living orangutan species.

Bornean orangutans spend more time in trees than any other great ape. Their diet includes fruit, seeds, flowers, tree sap, vines, and occasionally bird eggs. Adult males are much larger than females and may develop broad cheek pads called flanges, which help create their distinctive appearance.

The answer is sometimes confused with the Sumatran orangutan or Tapanuli orangutan, both of which are separate species with ranges outside Borneo. Orangutans once lived across much more of Southeast Asia, but today the Bornean species is restricted to fragmented forest habitats. It is Critically Endangered because of deforestation, plantation expansion, hunting, and habitat degradation.