Remus Lupin
Reasoning: The card of solitude, introspection, and learning by oneself. It can represent a wise teacher usually seen alone. Taking time to think, analyze and understand, all by oneself. Who better to represent this than Remus, who keeps to himself both because of his lycanthropy and by choice. He spends the entire year at Hogwarts examining himself and his choices alone, occasionally offering assistance and wisdom to Harry.
In a traditional tarot deck, this is the Hermit.
Notes
This card uses a drawing of Lupin that is a couple of years old, but is still one of my favorites I've done. So he was refined just a bit, and recycled to this new tarot card. Originally he had the boggart-moon emerging from his wand, but that didn't make a whole lot of sense, and just kind of felt in the way. So the (not-quite-full, of course...) moon was transferred to its rightful place in the night sky.