Dated back before the Inquisition, these witch hunters were very rare and elusive. Women who were trained at birth to hunt and kill witches.
They usually kill their victims, and make it appear to be a suicide or a natural death. One of their abilities is their being able to recognize a witch by sight.
According to the stories they had begun as a supernatural race called the Benandanti, which had been a small race of demon hunters. However they had also been known to go after any supernatural who used their powers for evil. They no longer exist, however, and according to some legends it is because they had been wiped out by the witch hunters.
The witch hunters were priestesses who held absolute power over their people with garden-variety magics. The sort of magic any street magician knows. Their people were believed to have started trading with tribes, such as the Benandantis.
The Benandantis did not care for the priestesses, and when the women learned the Benandantis were true supernaturals, they wiped them out. Believing that they were the very things they fought against.
After having successfully wiped out the Benandantis, which had taken then several centuries, they preistesses slid into their role, believing they were the true righteous ones ridding the world of evil spell-casters.
Their society of women spend their childhood preparing for the day they would come of age and kill a witch, or more should they be lucky enough.
There are very few families remaining. According to Annette Tucker, the previous generation has ended their following of the old ways and they no longer kill Witches, and instead of targeting all witches only target bad ones. Even then they prefer non-lethal ways.
Yet when speaking to Veronica Tucker, Savannah Levine is told that everything Annette told her was a lie. While the other families may have stopped carrying on with the old traditions, their family secretly continues to follow the old ways.