The Tau Empire is a rapidly expanding alien stellar empire situated within the Imperium of Man's Ultima Segmentum, near the Eastern Fringes of the Milky Way Galaxy. The Tau Empire was founded by the Tau caste called the Ethereals, who lead the Tau Empire in the name of the philosophy they have named the Greater Good. Several intelligent alien races (the Kroot, Vespid, Nicassar, Demiurg and even some humans who have turned their backs on the Imperium, known as Gue'vesa in the Tau Lexicon) have allied themselves with the Tau. The Tau Empire borders the Imperium of Man, and lies within the reach of the Astronomican. It has suffered many raids from the Orks, and also seems to lie in the path of several Tyranid splinter fleets of Hive Fleet Kraken.