Aun'Shi
He is awesome.
That is all.
What, you want more?
Really?
Do I have to?
Fine.
The Bringer of Victory, Aun'Shi
Aun'Shi is a Tau Ethereal, the philospher-warrior-monks who lead the Tau Empire down the path of enlightenment (or at least that's what they think of it as). His name literally means "victory."
Alongside just being generally charismatic, Aun'Shi has mastered the art of duelling with the honour blade, that weird two-bladed staff that the Ethereals carry (and for some reason only the Ethereals; seriously, mount a power version on a battlesuit, it'd be badass). (Melee combat is considered an outdated and barbaric mode of war in the Tau Empire. I mean, shit, why slay things with swords like those Mont'au savages do when you have pulse rifles and fusion blasters and ion cannons? The Ethereals' honour blades are meant as symbols of office, not reliable weapons. Aun'Shi is an exception.)
History
Aun'Shi was on his last tour of 'duty' before retiring to a paradise world when he was sent to bolster/train the defenders of a relatively new colony named Kel'tyr, which was founded on a planet infested with Orks. Usually not a good idea, but the Tau had been doing well enough negotiating with the Orks with their Burst cannons and railguns.
Unfortunately, as he was completing his tour of duty in the Fio'Vash, a horde of Orks surrounded the compound, besieging the Tau, and beheading their leader. As the Fire Caste began to run around like headless chickens with the death of the their leader, Aun'Shi proved himself to be stone-cold, leaping into action and splitting the Ork Warboss in half from scalp to groin, his honour blade stopping just above the ground as the Warboss fell to pieces. However, the Ork Hordes rallied and began to send wave after wave of Boyz at the compound, where Aun'Shi set himself in a bottleneck and just killed each Ork as they rammed themselves against the door like a particularly bloodthirsty Laurel & Hardy sketch.
When a relief force finally arrived at the besieged compound, they found the Orkz scattered to the winds, piles of of Greenskin corpses choking the entrance to the last standing building where Aun'Shi stood in the doorway, his blade soaked in ichor and gore as the last few surviving civilians huddled behind him. Because he was so badass for what basically amounts to a 60 year-old-man by Tau standards, Aun'Va (The Tau Space Pope) decided to revoke his retirement, and put him into the Tau warforce permanently, where he has been elevated to the position of a living miracle, and bringer of victory, mostly because he has never stopped hitting people with his bladed stick.
Tabletop
Aun'Shi is one of two Tau units that you actually want to be in an assault (the other being Commander Farsight). He brings both his interesting melee style and a re-rollable 4++ Invulnerable Save, alongside an Ethereal's massive Bubble of Buffs. However he's not overly competitive, and more just a fluffy character to be used if you've got points to sink on an Ethereal that might need to be more survivable. I wouldn't skip him over, but use him for casual play at most.