Madeline, the Arch-Heretic

The forgotten Heretic of Gaul

Once upon a time, Madeline wasn't named Madeline, and she lived in a place not yet called France. She did not believe in the religion the Romans had brought. She did not believe in the religion the old crones spoke of by fireside.
She found power in disbelief, and shared that power.

Before she was executed, most of the skin on her back was removed to preserve a tattoo there, which described the ways her cult had found their powers.

After being locked in a burning coffin in Hell for centuries, she's a bit hazy on those details, though.