Exarch

Exarchs are the leaders of the Eldar Aspect Shrines on the Craftworlds and lead the warriors of Khaine both in the worship of their god and on the battle field as warriors without peer.

All Craftworld Eldar practice the Paths, forms of mental concentration to focus their immense emotions into a task so they are not overwhelmed by sensation like their ancestors were and fall prey to Slaanesh, the god born from the ancient Eldar's excesses and rampant kinkiness. There is a danger though; an Eldar may become obsessed with achieving perfection along a path and become fixated on it, unable to ever follow another path again. They become referred to being lost on the path and are treated with a strange sense of loss from other Eldar for this, although many masters of the different paths are also widely respected.

Eldar who find they like killing too much and who become stuck on one of the warrior paths are referred to as Exarchs, Eldar who become the greatest experts of that particular kind of warfare on their Craftworld. They are given powerful weapons and armour usually kept within the temples and master skills through long experience, which they pass onto other Eldar who take up position for a time in the temple. Exarchs act as priests of Khaine as much as warriors, for they are the chosen holy warriors of the bloody handed god.

On the battlefield they can really wreck your shit up as they can possess skills that make their squads as a whole all that more useful and deadly. Of course this is countered by them costing an arm and leg in points but used rightly and they will mow down the competition.

They have another, less pleasant duty. When the need is dire and the Avatar of Khaine must be awoken to help the Craftworld, it requires the sacrifice of an Exarch anointed the young king, who will help the god to manifest for a time. So the exarch chosen as the young king makes the ultimate sacrifice, as they give themselves body and soul to allow their burning god to step forth once more, to grind the enemies of the Eldar underfoot.

Many exarches tend to die in some horrible/vain/glorious way in the fluff, just to make whoever it is they're fighting seem even more badass, a distinction they share with the Avatar and Terminator sergeants.