Daspletosaurus (/dæsˌpliːtəˈsɔːrəs/ das-PLEET-ə-SOR-əs; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 77 and 74.4 million years ago, during the Late Cretaceous Period. The genus Daspletosaurus contains three named species. Fossils of the earlier type species, D. torosus, have been found in Alberta, while fossils of a later species, D. horneri, have been found in Montana and Alberta. D. wilsoni has been suggested as an intermediate species between D. torosus and D. horneri that evolved through anagenesis, though further research may be required to definitively support the theory.

There are also multiple specimens which may represent new species of Daspletosaurus from Alberta and Montana, but these have not been formally described. The taxon Thanatotheristes has been suggested to represent a species of Daspletosaurus, D. degrootorum, but this has not been widely supported. Daspletosaurus is closely related to the much larger and more recent tyrannosaurid Tyrannosaurus. Like most tyrannosaurids, Daspletosaurus was a large bipedal predator, with the average adult measuring 8.5–9 m (28–30 ft) and weighing 2–3 metric tons (2.2–3.3 short tons). Daspletosaurus had the small forelimbs typical of tyrannosaurids, although they were proportionately longer than in other genera.

As an apex predator equipped with dozens of large, sharp teeth, Daspletosaurus was at the top of the food chain, probably preying on large dinosaurs like the ceratopsid Centrosaurus and the hadrosaur Hypacrosaurus. In some areas, Daspletosaurus coexisted with another tyrannosaurid, Gorgosaurus, though there is some evidence of niche differentiation between the two. While Daspletosaurus fossils are not as common as other tyrannosaurid fossils, the available specimens allow some analysis of the biology of these animals, including social behavior, diet, and life history.

The type specimen of Daspletosaurus torosus (CMN 8506) is a partial skeleton including the skull, the shoulder, a forelimb, the pelvis, a femur, and all of the vertebrae from the neck, torso, and hip, as well as the first eleven tail vertebrae. It was discovered in 1921 near Steveville, Alberta, by Charles Mortram Sternberg, who thought it was a new species of Gorgosaurus. It was not until 1970 that the specimen was fully described by Dale Russell, who made it the type of a new genus, Daspletosaurus, from the Greek δασπλής (dasplēs, stem and connective vowel resulting in dasplēto-) ("frightful") and σαυρος (sauros) ("lizard"). The type species is Daspletosaurus torosus, the specific name torosus being Latin for 'muscular' or 'brawny'. Aside from the type, there is only one other well-known specimen, RTMP 2001.36.1, a relatively complete skeleton discovered in 2001. Both specimens were recovered from the Oldman Formation in the Judith River Group of Alberta. The Oldman Formation was deposited during the middle Campanian stage of the Late Cretaceous, from about 79.5 to 77 Ma (million years ago).

Dale Russell also suggested that a specimen of an immature Albertosaurus (CMN 11315) from the younger Horseshoe Canyon Formation in Alberta actually belonged to a third specimen of Daspletosaurus as D. cf. torosus, extending the temporal range of the genus by approximately 3.5 million years into the Maastrichtian. He based this referral on features of its limb and pelvic girdle, as well as the curvature of the hand claws, which he interpreted as traits matching Daspletosaurus. This reassignment was not universally accepted, and thorough re-examination of the specimen favored its initial referral to Albertosaurus sarcophagus, despite lacking many of the diagnostic skeletal traits used to identify mature tyrannosaurids. An additional maxilla and various teeth from an Edmontosaurus-dominated bonebed in the Horseshoe Canyon Formation was also mistakenly referred to Daspletosaurus, but all the tyrannosaurid material has all since been confirmed to belong to Albertosaurus.

Over the years, various additional species have been assigned to the genus Daspletosaurus. Though some have been designated as Daspletosaurus spp, this does not imply that they all represent the same species.

Along with the holotype, Russell designated a specimen collected by Barnum Brown in 1913 as the paratype of D. torosus. This specimen (AMNH 5438) consists of parts of the hindleg, the pelvis, and some of its associated vertebrae. It was discovered in the Dinosaur Park Formation in Alberta. The Dinosaur Park Formation was formerly known as the Upper Oldman Formation and dates back to the middle Campanian, between 76.5 and 74.8 million years ago. Daspletosaurus fossils are known specifically from the middle to upper section of the formation, between 75.6 and 75.0 million years ago. In 1914, Brown collected a nearly complete skeleton and skull; forty years later his American Museum of Natural History sold this specimen to the Field Museum of Natural History in Chicago. It was mounted for display in Chicago and labeled as Albertosaurus libratus for many years, but after several skull features were later found to be modeled in plaster, including most of the teeth, the specimen (FMNH PR308) was reassigned to Daspletosaurus torosus by Thomas Carr in 1999. A total of eight specimens have been collected from the Dinosaur Park Formation over the years since, most of them within the boundaries of Dinosaur Provincial Park. Phil Currie believes that the Dinosaur Park specimens represent a new species of Daspletosaurus, distinguished by certain features of the skull. Pictures of this new species have been published, but it still awaits a name and full description in print. In 2024, Warshaw and colleagues suggested that the Dinosaur Park specimens likely belong to D. wilsoni. In 2025, Coppock and colleagues referred the Dinosaur Park Formation specimen CMN 350, a partial skull and skeleton with left dentary (TMP 2010.121.0001), to D. horneri.

A new tyrannosaurid specimen (OMNH 10131), including skull fragments, ribs, and parts of the hindlimb, was reported from New Mexico in 1990 and assigned to the now-defunct genus Aublysodon. Many later authors have reassigned this specimen, along with a few others from New Mexico, to yet another unnamed species of Daspletosaurus. However, research published in 2010 showed that this species, from the Hunter Wash Member of the Kirtland Formation, is actually a more primitive tyrannosauroid, and was classified in the genus Bistahieversor.