The woolly rhinoceros (Coelodonta antiquitatis) is an extinct species of rhinoceros that inhabited northern Eurasia during the Pleistocene epoch. The woolly rhinoceros was large, comparable in size to the largest living rhinoceros species, the white rhinoceros (Ceratotherium simum), and covered with long, thick hair that allowed it to survive in the extremely cold, harsh mammoth steppe. It had a massive hump reaching from its shoulder and fed mainly on herbaceous plants that grew in the steppe. Mummified carcasses preserved in permafrost and many bone remains of woolly rhinoceroses have been found. Images of woolly rhinoceroses are found among cave paintings in Europe and Asia, and evidence has been found suggesting that the species was hunted by humans. Like other Pleistocene megafauna, the species became extinct as part of the end-Pleistocene extinction event. The range of the woolly rhinoceros contracted towards Siberia beginning around 17,000 years ago, with the youngest reliable records being around 14,000 years old in northeast Siberia, coinciding with the Bølling–Allerød warming, which likely disrupted its habitat, with environmental DNA records possibly extending the range of the species around 9,800 years ago. Its closest living relative is the Sumatran rhinoceros (Dicerorhinus sumatrensis).

Woolly rhinoceros remains have been known long before the species was described and were the basis for some mythical creatures. Native peoples of Siberia believed their horns were the claws of giant birds. A rhinoceros skull was found in Klagenfurt, Austria, in 1335, and was believed to be that of a dragon. In 1590, it was used as the basis for the head on a statue of a lindworm. Gotthilf Heinrich von Schubert maintained the belief that the horns were the claws of giant birds, and classified the animal under the name Gryphus antiquitatis, meaning "griffin of antiquity".

One of the earliest scientific descriptions of an ancient rhinoceros species was made in 1769, when the naturalist Peter Simon Pallas wrote a report on his expeditions to Siberia where he found a skull and two horns in the permafrost. In 1772, Pallas acquired a head and two legs of a rhinoceros from the locals in Irkutsk, and named the species Rhinoceros lenenesis (after the Lena River). In 1799, Johann Friedrich Blumenbach studied rhinoceros bones from the collection of the University of Göttingen, and proposed the scientific name Rhinoceros antiquitatis. The geologist Heinrich Georg Bronn moved the species to Coelodonta in 1831 because of its differences in dental formation with members of the Rhinoceros genus. This name comes from the Greek words κοιλος (koilos, "hollow") and ὀδούς (odoús "tooth"), from the depression in the rhino's molar structure, giving the scientific name Coelodonta antiquitatis, "hollow-tooth of antiquity".

The woolly rhinoceros was the most recent species of the genus Coelodonta. The closest living relative of Coelodonta is the Sumatran rhinoceros, and the genus is also closely related to the extinct genus Stephanorhinus. A cladogram showing the relationships of C. antiquitatis to other Late Pleistocene-recent rhinoceros species based on genomic data is given below.

Relationships of the woolly rhinoceros based on morphology, excluding African rhinoceros species:

The ancestors of Coelodonta are suggested to have diverged from those of the Sumatran rhinoceros around 9.4 million years ago, with Coelodonta diverging from Stephanorhinus around 5.5 million years ago. The oldest known species of Coelodonta, Coelodonta thibetana is known from the Pliocene of Tibet dating to approximately 3.7 million years ago, with the genus being present in Siberia, Mongolia, and China during the Early Pleistocene. The woolly rhinoceros first appeared during the early Middle Pleistocene in China, and the oldest remains of the species in Europe, which represents the only species of Coelodonta to have been present in the region, date to approximately 450,000 years ago. The woolly rhinoceros is divided into two chrono-subspecies, with C. a. praecursor from the middle Pleistocene and C. a. antiquitatis from the late Pleistocene. Mitochondrial genomes suggest that the last mitochondrial ancestor of Late Pleistocene woolly rhinoceroses lived around 570,000 years ago.

An adult woolly rhinoceros typically measured 3.2 to 3.6 metres (10.5 to 11.8 ft) from head to tail, stood 1.45–1.6 metres (4.8–5.2 ft) tall at the shoulder, and weighed up to 1.5–2 metric tons (1.7–2.2 short tons) (with some sources placing the body mass of the species as high as 2.4–2.9 metric tons (5,300–6,400 lb)) making it comparable in size to the largest living rhinoceros species, the white rhinoceros (Ceratotherium simum). Compared to other rhinoceroses, the woolly rhinoceros had a longer head and body, and shorter legs.

Like the living white rhinoceros, the shoulder was at least sometimes raised with a substantial hump, which may have developed to support the weight of the animals large head and horns. Unlike the hump of the white rhinoceros, the hump of the woolly rhinoceros contained substantial fat reserves (probably predominantly white fat), the most substantial on the entire body. The hump likely served for thermoregulation (reducing the surface-area-to-volume ratio to make keeping the body warm more efficient) and/or as a storage for energy gained during warmer months to use during cold months. Aside from depictions in cave paintings, a hump is only definitively known from a single mummified subadult specimen (around 4-4.5 years old), and it is possible that the hump was a juvenile only feature or that the size/presence of the hump varied seasonally.