Tranquil

The Rite of Tranquility (involving the use of a magical brand made of lyrium) cuts off a mage's connection to the Fade -- they can no longer dream. As a side effect, their emotional center is utterly removed. One or both of these things make it so that demons can no longer possess them (it's not certain which).

If the Circle of Magi find a mage too weak of will to survive a demonic possession, tranquiling them is considered an act of kindness.

The tranquil use lyrium to enchant items, providing the Circle its main source of funding. They have no innate resistance to its effects, but they possess a level of concentration far beyond a normal person's are so are less likely to make a mistake while handling it.