The orangutan was originally thought to be just one species, but in 1996 they were divided into two separate species: the Bornean orangutan (which can be divided into three subspecies) and the Sumatran orangutan. They are of the genus Pongo and the only surviving species of the subfamily Ponginae.

The orangutan is the most solitary and the most arboreal (they spend most of their time in the trees) of the great apes. They have long reddish-brown hair. Males are typical twice as large as females and have throat pouches which allow them to make loud calls. Dominant males have distinctive cheek pads.

They are among the most intelligent of the apes, utilizing a number of sophisticated tools and creating elaborate sleeping nests every night. They may also have distinct cultures from one group to the next. Their diet consists mainly of fruit, but will also eat vegetation, bark, honey, insects, and bird eggs. Both species are considered Endangered, with the Sumatran orangutan being Critically Endangered.