The Chitauri are aliens of unknown origin from the Marvel Comics movie franchise.
Chitauri are humanoids. Their strength and durability seems to be slightly above that of a fit human. Beyond that, they do not seem to have exceptional attributes. Many of their physical advantages appear to be cybernetic, with power or control dependent upon a remote source.
The Chitauri appear to be ruled in a dictatorial fashion, although the details are unclear.
The Chitauri have access to powerful directed-energy weapons: the energy delivered by a shot appears to be comparable to a stick of dynamite, but it doesn't appear to have strong penetration. Chitauri also have flying vehicles which can easily hover, indicating that they have the ability to manipulate (or otherwise defy) gravity. They also control "Leviathans", which are trained creatures of immense size that they use as mounts. Leviathans can fly, and they are enclosed in durable, articulated armor that can resist advanced anti-tank weapons.
There is no evidence of a Chitauri space fleet, so the threat they pose to other civilizations does not appear to be particularly great. They are seeking advanced interstellar/intergalactic teleportation technology to achieve their conquest goals.