There are many legends of great heroes battling the forces of darkness, usually in the form of one monster or another. Knights vs. Dragons. Priests vs. Demons. Other things that involved a hero battling evil. Well, the legends had to start somewhere. These legends are part of a struggle as old as time itself, a war between the light and the dark waged in secret.
In the early mists of history, a group of people arose whose membership extended beyond nationality, religion, language, beliefs, and gender. They called themselves the Hunters. They took it upon themselves to fight evil in all of it's forms. No one knew who would become a Hunter until their skills began manifesting, except for those rare few with certain gifts. Hunters were always athletic, strong, and had incredible reflexes. They also possessed the ability to recognize creatures of evil for what they were, no matter what form they took. A subset of the Hunters were also gifted with Sight, and could predict things and locate other Hunters. And Hunters always instinctively knew their own. They were also gifted with nigh-immortality and a talent for magic.
But they also had weaknesses, and immortality was not the same thing as invincibility. The Hunters are more or less Fey creatures. Cold iron will burn them, knowing their true name will grant power over them. And the forces of evil always know them for what they are. Even before the Hunters themselves do. And, like any sort of protector, there are never nearly enough.
Hunters, once recognized, are loosely orgainzed into clans, based on talents and other things, but not necessarily blood relationships. Clan Camdaelen is the clan of the strategists, and are usually descended from great military leaders. Clan T'willyth is the warrior clan, and many famous knights are counted in the ranks. Clan Dracis is the clan of the mages, those especially gifted at magic. And the Seers are Clan Veritas. Each clan is lead by a clan lord, who is usually the oldest and most experienced member of the clan. Though it is rare, women can be clan lords as well.
There is another clan, but no one speaks of it, for the members are the Fallen, the Hunters who have sided with the very forces they were meant to fight. They are accursed outcasts, and very dangerous. The most feared of the Fallen is the Black Seeker, the only Seer to ever have turned to evil.
Since the age-old evils of a supernatural nature have always had human servants, the Hunters do their best to keep their existance secret. Sometimes, their efforts are for naught, and the activities of a Hunter become common knowledge. Some are feared and hated for this; some are revered as saints and heroes. It also suits the purpose of evil beings for their own presence to remain secret. So ordinarily, most people do not have any knowledge of either force, and dismiss stories of such as mere myth.