Ur-priest

Ur-priests were evil spellcasters of divine magic who despised deities and believed that they obtained their power by stealing it from them. Though in actuality, ur-priests unknowingly received their spells from deities just like any other priest.

Culture
Deities treated ur-priests as free agents, a sort of wild card whose results they could benefit from. However, if a deity found that an ur-priest was no longer benefiting them they would stop the flow of spells to them. In ancient times the deities Gargauth, Leira, and Talos engaged in this practice. In the Present Age both Gargauth and Talos continued to use ur-priests, though supported only a few isolated individuals and limited what spells they could gain.

Ur-priests frequently worked alone, although ocassionaly found partnerships to be useful. They did not congregate together in temples, as they feared it might draw unwanted attention from the divine.

Clerics and other true divine spellcasters viewed ur-priests them as abominations and ur-priests viewed them as lackeys, thus the two groups rarely associated with each other. If priests ever fought an ur-priest who was being granted spells by the same deity, the god would deprive the latter of their power, leading to a public vanquishment that would enhance the deity's reputation among the public.

Abilities
Rather than praying each day for their spells, ur-priests went into a trance and committed what they assumed to be cunningly siponing off an unnoticable degree of divine power from a deity. They could become quite powerful, though they never had as diverse an array of spells as a true cleric. They also had some degree of resistance against divine spells.

The most powerful of ur-priests were said to be capable of stealing the spell-like abilities of other creatures, like stealing a pit fiend's teleport without error.