Humans in the Tau Empire
Known as Gue'la in the Tau lexicon, this species is the most populous in Tau territory save for the Tau themselves. This is unsurprising as large portions of the Tau's current realm was once Imperial and their border worlds with the Imperium Tertius are of course populated with humans. This is of course forgetting the millennia of absorbing human worlds that occurred before the end of the Imperium.
It is important to explain the history of many of the human worlds within Tau space. In the aftermath of the Emperor's death the Tau empire expanded rapidly confused to find the mighty behemoth that they had warred with for so long collapsing as they looked on. With this general collapse came famine, plagues, wars and death. The Tau intervened.
It has been argued that the Tau could have intervened before the situation spiralled out of control, it can also be argued that the human governors would have likely never accepted in the first place due to their paranoid xenophobia and so the rabbit hole of "what ifs" continue. The fact of the matter is that the Tau did intervene, and that intervention saved trillions of lives. The Tau restored, order, they filled bellies that were empty, stomped out the threats that had come down upon them and all they asked in exchange was for the humans to follow the Greater Good.
As such in many Tau territories you will find worlds that are predominantly human and will find humans in every level of Tau society, researchers, warriors, workers, teachers, artists, diplomats etc. except for the Ethereals. Even then you can find humans as scribes and assistants to the leaders of the Greater Good, serving alongside Tau of all castes.
Indeed Commander Brightmoon, one of the Tau's best commanders at the moment is a human.
This dedication has given these humans a new name. From Gue'vesa, which means Human Helper, to Lor, Multi caste. This effectively acknowledges humans as another caste within the Tau Empire and a critical part of the Greater Good due to their contributions and essential nature.
However, the honour of being a member of the Lor, is not given to every human as there are still many who refuse to assimilate, especially the ones in the still very xenophobic Ultramar as captured border worlds consider those assimilated by the Tau to be heretics on par with Chaos Cultists themselves.
Unknown to Ultramar, due to the Tau carefully ensuring that they are kept as far away from the Western Front as possible, the Tau have successfully managed to implant geneseed and create their own astartes that fight for the Greater Good. This was the culmination of a project that took centuries as they were never able to successfully capture an Apothecary and the inner workings of geneseed are as much a mystery to the Tau as they are to everyone who isn't the Emperor and his sons, forcing them to opt for a brute force method of study. This method has led to numerous imperfections with the process, from relatively minor things like a non functional Bletchers gland, to more major psychological issues due to not having access to the correct techniques to condition the new astartes. These are flaws which the Tau are attempting to correct.
Regardless the Tau's patience and dedication was rewarded and the first Lor astartes were born. Clad in full Tau equipment and benefiting from the expertise and training of the entire empire, these battlesuit clad champions are proving decisive in the Tau's wars against the Orks, despite not matching up to their Ultramar counterparts.
@Durin