High Priest

Although hardly seen or even mentioned in the series, there are Warlocks that serve the Old Religion. Followers of the Old Religion that are more commonly referred to are the High Priestesses. These could be either good or bad, they may use Magic for good reasons, or for selfish and evil reasons.

High priests that are known to be, or may one day be are:

Merlin,(maybe sometime in the future)

Mordred,(possibly)

Alator of the Catha,(definately)

Gaius,(possibly sometime in the past. Although he may have been their servants)

Alvarr,(very unlikely).

There may not be as many High Priests as there are High Priestesses.