Orangutans are primates of the genus Pongo, an ape species native on Earth to Indonesia and Malaysia. They are of the family Hominidae, which also includes gorillas, chimpanzees, and humans, species which characteristically walk on two legs, have a large brain-to-body mass ratio, and rely on vision as their primary sense. Sentient, highly-intelligent orangutans exist on at least one alternate Earth.
During Captain James T. Kirk's five-year mission, the USS Enterprise encountered several intelligent ape species on an alternate Earth. Orangutan Doctor Zaius was a prominent member of that region's government, which presided over a civilization of chimpanzees, orangutans and gorillas, and subjugated bands of non-intelligent humans. Commander Kor conspired to make that government more receptive to a Klingon alliance by empowering gorilla General Marius. (TOS comic: "The Primate Directive")