The 'Sumatran Rhinoceros (Dicerorhinus sumatrensis) is a member of the family Rhinocerotidae and one of five extant rhinoceroses. It is the smallest rhinoceros, standing about 120–145 centimetres (3.9–4.8 ft) high at the shoulder, with a body length of and weight of 500–800 kilograms (1100–1760 lb). Like the African species, it has two horns; the larger is the nasal horn, typically 15–25 centimetres (6–10 in), while the other horn is typically a stub. A coat of reddish-brown hair covers most of the Sumatran Rhino's body.

Members of the species once ranged through rainforests, swamps and cloud forests in India, Burma, Thailand, Malaysia and islands in Indonesia. They are now critically endangered with only six substantial populations in the wild: four on Sumatra, one on Borneo, and one on peninsular Malaysia. Their numbers are difficult to determine because they are solitary animals and widely scattered across their range, but they are estimated to number around 300. The decline in the number of Sumatran Rhinoceros is attributed primarily to poaching for their horns, which are highly valued in traditional Chinese medicine, fetching as much as US$30,000 per kilogram on the black market. The rhinos have also suffered from habitat loss as their forests have been cleared for lumber and conversion to agriculture.

The Sumatran Rhino is a mostly solitary animal except for courtship and child-rearing. It is the most vocal rhino species and also communicates through marking soil with its feet, twisting saplings into patterns, and leaving excrement. The species is much better studied than the similarly reclusive Javan Rhinoceros, in part because of a program that brought 40 Sumatran Rhinos into captivity with the goal of preserving the species. The program was considered a disaster even by its initiators, with most of the rhinos dying and no offspring being produced for nearly 20 years, an even worse decline than in the wild.