He is Sauron. She is the Baba Yaga. He is Voldemort. She is the Wicked Witch of the West.
He is a man. She is a woman. Neither is truly human.
They have vast power but their power is illegitimate and unholy. It was bought at the price of their soul.
They know things that Man Was not Meant to Know. This knowledge has corroded any remnants that have remained of their souls.
He is not to be confused with The Wizard who is a Mentor who knows magic.
If she is a woman, she is either a hag or inhumanely beautiful. If she is beautiful, she is only beautiful by virtue of her magic. She is, in truth, a hag.
He is old. If he appears to be young it is because he has used magic to preserve himself. Once the spell is broken he will be proven to be old and withered.
They are asexual. The only sexual acts that they will ever engage in will be as part of a dark rite. Any such acts will be perverse, shocking and blasphemous.
They have sold their souls to dark forces. They are damned and beyond any hope of redemption.
Although they have vast power, they will always crave more power, especially over others. This is the instrument of their downfall.
They believe in Good but they hate it. They hate it will a personal passion. Their choice to be Evil is deliberate and fulfilling.
They are sadistic. It is not sufficient to kill one’s enemies; they must be made to suffer.
They are Satanists. Even if they don’t worship Satan, himself, they worship Evil, which is the same thing.