The Tau (or T'au) are a race of humanoid aliens in Warhammer 40k. They have ice-blue skin, hooves similar to those of a Terran ungulate, and curiously lack noses - instead a 'slit' in their face acts as an olfactory organ. Originating from the world of T'au, when Adeptus Mechanicus explorators first discovered the world in M35 their existence was one of a paleolithic people. In the intervening 5-6000 years since the initial discovery, the Tau have undergone an extremely rapid technological advancement - according to Tau legend, this was directly following the great species-wide 'civil war' known as the Tau'va which saw the aliens almost extirpate themselves.
The Tau of M41 are divided into castes, each named for an element plus the Ethereal caste. The Fire caste serve as warriors; the Water caste act as diplomats, translators, and negotiators; the Earth caste are engineers, architects, and other such professionals, overseeing works done by drone labourers; the Air caste support all others as pilots and crew of space-borne craft; and finally the Ethereal caste act as rulers. The castes are separate but valued equally.
