An Exarch is a former Aspect Warrior who has lost himself upon the Path of the Warrior and is unable to ever leave it again. At this point he is considered to have abandoned the greater Eldar Path with its promise of new experience and constant development in favour of a life of bloodshed. He becomes an Exarch; simultaneously a priest of Kaela Mensha Khaine, a caretaker of the individual warrior shrine, and trainer, teacher, and instructor of the respective aspect. He is equipped with very ancient weaponry and armour. Each warrior aspect has its own particular kind of Exarchs. On the battlefield an Exarch commands a individual squad of aspect warriors. Exarchs are formidable opponents, and most of them can use their abilities to help the whole squad of aspect warriors under their command. The very first original Exarchs are the Phoenix Lords.
Exarchs are regarded with both awe and revulsion by other Eldar. Awe, because Exarchs single-mindedly pursue a side of their nature which most Eldar fear to even contemplate. Revulsion, because they have become trapped in the warrior aspect and destined for a life of never-ending violence.3
An Exarch assumes an ancient name associated with the Aspect. Each name is associated with a set of Exarch armour the Exarch wears in battle. If the Exarch is killed another Exarch may take the suit and the name. The same armour is worn by many successive Exarchs over thousands of years. The Exarch breaks with his old life, continuing the legendary life of the single heroic identity represented by that armour and name. Worked into the armour is the spirit stone containing the spirit of the very first hero to have worn it. When the Exarch enters the armour this spirit merges with his own, adding its own accumulated memories and experiences to his.3