orangutan, an ape, Pongo pygmaeus, found in swampy coastal forests of Borneo and Sumatra. Highly specialized for arboreal life, it usually travels by grasping branches with hands and feet and moving from tree to tree. Adult males are about 41/2 ft (1.4 m) tall and weigh up to 180 lbs (82 kg). Their arms are very long, the total span sometimes exceeding 7 ft (2.1 m). Their legs are short and bowed, making ground travel awkward; they walk with a side-to-side shuffle on all fours. The body is rotund and covered with long hair in various shades of red. The face of a young orangutan looks quite human; the name means "forest person" in Malay. Old males usually develop large cheek pads and facial hair that resembles a man's moustache and beard. Enormous throat pouches also develop with sexual maturation, which starts at about age 14.

Adult orangutans are basically solitary, except for mother-offspring pairs; however, weaned juveniles sometimes congregate in small groups. Males are aggressive toward each other and fight over females. Individual nests are usually constructed in trees each night. Fruit is a diet mainstay, and orangutans are important seed distributors.

The numbers of orangutans have recently dropped precipitously owing to loss of habitat to deforestation (logging, forest fires, and clearing of land for plantations) and the killing of females for their young, to be sold as pets or zoo animals. Fewer than 30,000 individuals are believed to remain in the wild, and the species is listed as endangered. Orangutans are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Primates, family Pongidae.