The Tasmanian devil (Sarcophilus harrisii; palawa kani: purinina) is a carnivorous marsupial of the family Dasyuridae. It was formerly present across mainland Australia, but became extinct there around 3,500 years ago; it is now confined to the island of Tasmania. The size of a small dog, the Tasmanian devil became the largest carnivorous marsupial in the world following the extinction of the thylacine in 1936. It is related to quolls, and distantly related to the thylacine. It is characterised by its stocky and muscular build, black fur, pungent odour, extremely loud and disturbing screech, keen sense of smell, and ferocity when feeding. The Tasmanian devil's large head and neck allow it to generate among the strongest bites per unit body mass of any extant predatory land mammal. It hunts prey and scavenges on carrion.

Although devils are usually solitary, they sometimes eat and defecate together in a communal location. Unlike most other dasyurids, the devil thermoregulates effectively, and is active during the middle of the day without overheating. Despite its rotund appearance, it is capable of surprising speed and endurance, and can climb trees and swim across rivers. Devils are not monogamous. Males fight one another for females, and guard their partners to prevent female infidelity. Females can ovulate three times in as many weeks during the mating season, and 80% of two-year-old females are seen to be pregnant during the annual mating season.

Females average four breeding seasons in their life, and give birth to 20 to 30 live young after three weeks' gestation. The newborn are pink, lack fur, have indistinct facial features, and weigh around 0.20 g (0.0071 oz) at birth. As there are only four nipples in the pouch, competition is fierce, and few newborns survive. The young grow rapidly, and are ejected from the pouch after around 100 days, weighing roughly 200 g (7.1 oz). The young become independent after around nine months.

In 1941, devils became officially protected. Since the late 1990s, the devil facial tumour disease (DFTD) has drastically reduced the population and now threatens the survival of the species, which in 2008 was declared to be endangered. Starting in 2013, Tasmanian devils are again being sent to zoos around the world as part of the Australian government's Save the Tasmanian Devil Program. The devil is an iconic symbol of Tasmania and many organisations, groups and products associated with the state use the animal in their logos. It is seen as an important attractor of tourists to Tasmania and has come to worldwide attention through the Looney Tunes character of the same name.

Believing it to be a type of opossum, naturalist George Harris wrote the first published description of the Tasmanian devil in 1807, naming it Didelphis ursina, due to its bearlike characteristics such as the round ear. He had earlier made a presentation on the topic at the Zoological Society of London. However, that particular binomial name had been given to the common wombat (later reclassified as Vombatus ursinus) by George Shaw in 1800, and was hence unavailable. In 1838, a specimen was named Dasyurus laniarius by Richard Owen, but by 1877 he had relegated it to Sarcophilus. The modern Tasmanian devil was named Sarcophilus harrisii ("Harris's flesh-lover") by French naturalist Pierre Boitard in 1841.

A later revision of the devil's taxonomy, published in 1987, attempted to change the species name to Sarcophilus laniarius based on mainland fossil records of only a few animals. However, this was not accepted by the taxonomic community at large; the name S. harrisii has been retained and S. laniarius relegated to a fossil species. "Beelzebub's pup" was an early vernacular name given to it by the explorers of Tasmania, in reference to a religious figure who is a prince of hell and an assistant of Satan; the explorers first encountered the animal by hearing its far-reaching vocalisations at night. Related names that were used in the 19th century were Sarcophilus satanicus ("Satanic flesh-lover") and Diabolus ursinus ("bear devil"), all due to early misconceptions of the species as implacably vicious. The Tasmanian devil (Sarcophilus harrisii) belongs to the family Dasyuridae. The genus Sarcophilus contains two other species, known only from Pleistocene fossils: S. laniarius and S. moomaensis. Phylogenetic analysis shows that the Tasmanian devil is most closely related to quolls.

According to Pemberton, the possible ancestors of the devil may have needed to climb trees to acquire food, leading to a growth in size and the hopping gait of many marsupials. He speculated that these adaptations may have caused the contemporary devil's peculiar gait. The specific lineage of the Tasmanian devil is theorised to have emerged during the Miocene, molecular evidence suggesting a split from the ancestors of quolls between 10 and 15 million years ago, when severe climate change came to bear in Australia, transforming the climate from warm and moist to an arid, dry ice age, resulting in mass extinctions. As most of their prey died of the cold, only a few carnivores survived, including the ancestors of the quoll and thylacine. It is speculated that the devil lineage may have arisen at this time to fill a niche in the ecosystem, as a scavenger that disposed of carrion left behind by the selective-eating thylacine. The extinct Glaucodon ballaratensis of the Pliocene age has been dubbed an intermediate species between the quoll and devil.

Fossil deposits in limestone caves at Naracoorte, South Australia, dating to the Miocene include specimens of S. laniarius, which were around 15% larger and 50% heavier than modern devils. Older specimens believed to be 50–70,000 years old were found in Darling Downs in Queensland and in Western Australia. It is not clear whether the modern devil evolved from S. laniarius, or whether they coexisted at the time. Richard Owen argued for the latter hypothesis in the 19th century, based on fossils found in 1877 in New South Wales. Large bones attributed to S. moornaensis have been found in New South Wales, and it has been conjectured that these two extinct larger species may have hunted and scavenged. It is known that there were several genera of thylacine millions of years ago, and that they ranged in size, the smaller being more reliant on foraging. As the devil and thylacine are similar, the extinction of the co-existing thylacine genera has been cited as evidence for an analogous history for the devils. It has been speculated that the smaller size of S. laniarius and S. moornaensis allowed them to adapt to the changing conditions more effectively and survive longer than the corresponding thylacines. As the extinction of these two species came at a similar time to human habitation of Australia, hunting by humans and land clearance have been mooted as possible causes. Critics of this theory point out that as indigenous Australians only developed boomerangs and spears for hunting around 10,000 years ago, a critical fall in numbers due to systematic hunting is unlikely. They also point out that caves inhabited by Aborigines have a low proportion of bones and rock paintings of devils, and suggest that this is an indication that it was not a large part of indigenous lifestyle. A scientific report in 1910 claimed that Aborigines preferred the meat of herbivores rather than carnivores. The other main theory for the extinction was that it was due to the climate change brought on by the most recent ice age.