[4] Related words include "kula" from Georges River to Sydney's south and west, and "kulla" (or kūlla) among southeastern Queensland’s Dippil people.

[11]: 58–59  French naturalist Anselme Gaëtan Desmarest coined the name Phascolarctos fuscus in 1820, suggesting that the brown-coloured versions were a different species than the grey ones.

Other names suggested by European authors included Marodactylus cinereus by Goldfuss in 1820, P. flindersii by René Primevère Lesson in 1827, and P. koala by John Edward Gray in 1827.

[16] Like the modern species, prehistoric koalas had well developed ear structures, which suggests that they also made long-distance vocalisations and had a relatively inactive lifestyle.

The genus Phascolarctos split from Litokoala in the late Miocene,[15][17] and had several adaptations that allowed it to live on a eucalyptus diet: the palate shifted towards the front of the skull; the upper teeth were lined by thicker bone, molars became relatively low compared to the jaw joint and with more chewing surface; the pterygoid fossa shrank;[15] and a larger gap separated the incisor teeth and the molars.

A 2008 study questioned this hypothesis, noting that P. cinereus and P. stirtoni were sympatric during the mid-late Pleistocene, and that their teeth morphology displayed the major differences.

A 1999 genetic study suggests koalas exist as a cline within a single evolutionarily significant unit with limited gene flow between local populations.

[18]: 234 The koala has a broad, dark nose[36] with a good sense of smell, and it is known to sniff the oils of individual branchlets to assess their edibility.

[11]: 76  The animal's dentition consists of incisors and cheek teeth (a single premolar and four molars on each jaw) that are separated by a large gap (a characteristic feature of herbivorous mammals).

[23]: 49  They can digest the toxic plant secondary metabolites, phenolic compounds and terpenes due to their production of cytochrome P450, which neutralises these poisons in the liver.

[32] In semi-arid climates, they prefer riparian habitats, where nearby streams and creeks provide refuge during times of drought and extreme heat.

[44] Koalas are herbivorous, and while most of their diet consists of eucalypt leaves, they can be found in trees of other genera, such as Acacia, Allocasuarina, Callitris, Leptospermum, and Melaleuca.

[23]: 54–56 [50] Chest gland secretions are complex chemical mixtures — about 40 compounds were identified in one analysis — that vary in composition and concentration across season and age.

[23]: 62  After seven weeks, the joey has a proportionally large head, clear edges around its face, more colouration, and a visible pouch (if female) or scrotum (male).

[51] Koalas can breed every year if environmental conditions are good, though the long dependence of the young usually leads to year-long gaps in births.

[62] In a three-year study of almost 600 koalas taken to the Australia Zoo Wildlife Hospital in Queensland, 73.8% of the animals were infected with parasitic protozoal genus Trypanosoma, the most frequent of which was T. irwini.

Price encountered the "cullawine" on 26 January 1798, during an expedition to the Blue Mountains,[67] but his remarks would first be published in Historical Records of Australia, nearly a century later.

[2]: 8  In 1802, French-born explorer Francis Louis Barrallier encountered the animal when his two Aboriginal guides, returning from a hunt, brought back two koala feet they were intending to eat.

[2]: 9–10  Reports of the "Koolah" appeared in the Sydney Gazette in late 1803, and helped provide the impetus for King to send artist John Lewin to create watercolours of the animal.

[2]: 12–13 Botanist Robert Brown was the first to write a formal scientific description in 1803, based on a female specimen captured near what is now Mount Kembla in the Illawarra region of New South Wales.

[2]: 16–28  William Paterson, who had befriended Brown and Bauer during their stay in New South Wales, wrote an eyewitness report of his encounters with the animals and this would be the basis for British surgeon Everard Home's anatomical writings on them.

[2]: 37  Perry called it the "New Holland Sloth", and his dislike for the koala, evident in his description of the animal, was reflected in the contemporary British attitudes towards Australian animals as strange and primitive:[2]: 40 ...  the eye is placed like that of the Sloth, very close to the mouth and nose, which gives it a clumsy awkward appearance, and void of elegance in the combination ... they have little either in their character or appearance to interest the Naturalist or Philosopher.

As Nature however provides nothing in vain, we may suppose that even these torpid, senseless creatures are wisely intended to fill up one of the great links of the chain of animated nature ...[69]Naturalist and popular artist John Gould illustrated and described the koala in his three-volume work The Mammals of Australia (1845–1863) and introduced the species, as well as other members of Australia's little-known faunal community, to the public.

[2]: 94–96  English naturalist George Robert Waterhouse, curator of the Zoological Society of London, was the first to correctly classify the koala as a marsupial in the 1840s, and compared it to fossil species Diprotodon and Nototherium, which had been discovered just recently.

[2]: 46–48  Similarly, Gerard Krefft, curator of the Australian Museum in Sydney, noted evolutionary mechanisms at work when comparing the koala to fossil marsupials in his 1871 The Mammals of Australia.

As related by prosecutor to the society, William Alexander Forbes, the animal suffered an accidental demise when the heavy lid of a washstand fell on it and it was unable to free itself.

[2]: 216  According to biologist Stephen Jackson: "If you were to take a straw poll of the animal most closely associated with Australia, it's a fair bet that the koala would come out marginally in front of the kangaroo".

Created by Dorothy Wall in 1933, the character appeared in books, films, TV series, merchandise, and a 1986 environmental song by John Williamson.

[90] To reduce road deaths, government agencies have been exploring various wildlife crossing options,[91][92] such as the use of fencing to channel animals toward an underpass, in some cases adding a walkway to an existing culvert.

[88] In a 30-year retrospective study performed at a New South Wales koala rehabilitation centre, trauma was found to be the most frequent cause of admission, followed by symptoms of Chlamydia infection.