Genetic evidence suggests that the wolverine is most closely related to the tayra and martens, all of which shared a Eurasian ancestor.

There are two subspecies: the Old World form, Gulo gulo gulo, and the New World form, G. g. luscus. Some authors had described as many as four additional North American subspecies, including ones limited to Vancouver Island (G. g. vancouverensis) and the Kenai Peninsula in Alaska (G. g. katschemakensis). However, the most currently accepted taxonomy recognizes either the two continental subspecies or G. gulo as a single Holarctic taxon.
Recently compiled genetic evidence suggests most of North America's wolverines are descended from a single source, likely originating from Beringia during the last glaciation and rapidly expanding thereafter, though considerable uncertainty to this conclusion is due to the difficulty of collecting samples in the extremely depleted southern extent of the range.

Anatomically, the wolverine is an elongated animal that is low to the ground. With strong limbs, broad and rounded head, small eyes and short rounded ears, it most closely resembles a large fisher. Though its legs are short, its large, five-toed paws with crampon-like claws and plantigrade posture enable it to climb up and over steep cliffs, trees and snow-covered peaks with relative ease.

The adult wolverine is about the size of a medium dog, with a body length ranging from 65–109 cm (26–43 in); standing 36–45 cm (14–18 in) at the shoulder; and a tail length of 17–26 cm (6+1⁄2–10 in). Weight is usually 11–18 kg (24–40 lb) in males, and in females 8–12 kg (18–26 lb). Exceptionally large males of as much as 32 kg (71 lb) are referenced in Soviet literature, though such weights are deemed in Mammals of the Soviet Union to be improbable. The males are often 10–15% larger than the females in linear measurements and can be 30–40% greater in weight. According to some sources, Eurasian wolverines are claimed to be larger and heavier than those in North America, with weights of up to 20 kg (44 lb). However, this may refer more specifically to areas such as Siberia, as data from Fennoscandian wolverines shows they are typically around the same size as their American counterparts. It is the largest of terrestrial mustelids; only the marine-dwelling sea otter, the giant otter of the Amazon basin and the semi-aquatic African clawless otter are larger—while the European badger may reach a similar body mass, especially in autumn.

Wolverines have thick, dark, oily fur which is highly hydrophobic, making it resistant to frost. This has led to its traditional popularity among hunters and trappers as a lining in jackets and parkas in Arctic conditions. A light-silvery facial mask is distinct in some individuals, and a pale buff stripe runs laterally from the shoulders along the side and crossing the rump just above a 25–35 cm (10–14 in) bushy tail. Some individuals display prominent white hair patches on their throats or chests.

Like many other mustelids, it has potent anal scent glands used for marking territory and sexual signaling. The pungent odor has given rise to the nicknames "skunk bear" and "nasty cat." The anal gland secretion for the samples obtained from six animal's secretion was complex and variable: 123 compounds were detected in total, with the number per animal ranging from 45 to 71 compounds. Only six compounds were common to all extracts: 3-methylbutanoic acid, 2-methylbutanoic acid, phenylacetic acid, alpha-tocopherol, cholesterol, and a compound tentatively identified as 2-methyldecanoic acid. The highly odoriferous thietanes and dithiolanes found in anal gland secretions of some members of the Mustelinae [ferrets, mink, stoats, and weasels (Mustela spp.) and zorillas (Ictonyx spp.)…

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Wolverines live primarily in isolated arctic, boreal, and alpine regions of northern Canada, Alaska, Siberia, and Fennoscandia; they are also native to European Russia, the Baltic countries, the Russian Far East, northeast China and Mongolia.

Wolverine remains have been found in Ukraine, but they are extirpated there today and it is unclear whether the wolverines would have formed sustainable populations.

Unique records of encounters with wolverines have been noted in Latvia, the most recent one being in late July 2022 (although it can be disputed because of the unclear footage); the population was widespread in the 16th and 17th centuries, but nowadays it is not native to the area.

Most New World wolverines live in Canada and Alaska. However, wolverines were once recorded as also being present in Colorado, areas of the southwestern United States (Arizona and New Mexico), the Midwest (Indiana, Nebraska, North and South Dakota, Ohio, Minnesota, and Wisconsin), New England (Maine, New Hampshire, Vermont, and Massachusetts) and in New York and Pennsylvania.

In the Sierra Nevada, wolverines were sighted near Winnemucca Lake in spring 1995 and at Toe Jam Lake north of the Yosemite border in 1996; and later photographed by baited cameras, including in 2008 and 2009, near Lake Tahoe. According to a 2014 U.S. Fish and Wildlife Service publication, "wolverines are found in the North Cascades in Washington and the Northern Rocky Mountains in Idaho, Montana, Oregon (Wallowa Range), and Wyoming. Individual wolverines have also moved into historic range in the Sierra Nevada Mountains of California and the Southern Rocky Mountains of Colorado, but have not established breeding populations in these areas". In 2022, Colorado Parks and Wildlife considered plans to reintroduce the wolverine to the state.

Wolverines are also found in Utah but are very rarely seen, with only six confirmed sightings since the first confirmed sighting in 1979. Three of these six confirmed Utah sightings have been caught on video. A wolverine, a male, was finally captured and tagged in Utah in 2022 before being released back into the wild to better understand the animal's range.

In August 2020, the National Park Service reported that wolverines had been sighted at Mount Rainier, Washington, for the first time in more than a century. The sighting was of a reproductive female and her two offspring.

In 2004, the first confirmed sighting of a wolverine in Michiga…

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