Raptorex is a genus of primitive tyrannosauroid dinosaur, similar to (but much smaller than) the later tyrannosaurids such as Tyrannosaurus Rex. Its fossil remains consist of a single specimen uncovered in the lower Yixian Formation of northeastern China, dated to approximately 125 million years ago during the early Cretaceous period. The type species is R. kriegsteini, described in 2009 by Sereno et. al. The genus name is derived from Latin, raptor, "robber", and rex, "king". The specific name honours Roman Kriegstein in whose honor the specimen was secured for scientific study.
Raptorex shows the same basic proportions as later tyrannosauroids: a comparatively large and solidly-constructed skull, long legs with adaptations for running, and tiny, two-fingered forelimbs. This is in contrast with more basal, contemporary tyrannosauroids such as Dilong, which retained features characteristic of more basal other coelurosaurs such as a small head and long, three-fingered forelimbs.
Despite its similarity to later, giant tyrannosaurs, Raptorex was comparatively very small, estimated at 3 m (10 ft) long and about 65 kg (143 lb). The holotype (LH PV18) measured about 2.5 m (8 ft) and died in its sixth year.