the Tau hierarchial order along with a designation of a Tau's life. Tau from the fire (shas) caste are the defenders of Tau space. The air (kor) pilot the ships and man the stations. Earth caste build and engineer the weapons the fire caste carry and the ships the earth caste fly. The water caste liases and arbitrates. Without them, the Tau would have no allies. The final, most mysterious of the castes is the ethereal (aun). These lords and (psykers?) rule the Tau and put forth the greater good among the masses.
Aun'Shui is an renowned member of the ethereal caste.