I know he has short hair, glasses, brown eyes, and he wears robes. Last night I tried sketching him again. I think I might be sold on this.
Even though I wasn't certain what he looked like and he didn't have a name for the longest time, I pretty much new his personality and behavior.
He's sort of a traveling teacher. Well known among magic users in Astraea. He is skilled in magic, but certainly not the most powerful. He's mainly skilled in how easy it is for him to use it. So while he might lack in force/power in terms of magic, he makes up for in speed. He's also more skilled with the dead and spirit world.
Theo also believes that knowledge and intelligence is a person's greatest strength and books are his favorite thing. He's often found in a library if he isn't teaching people.
He's kind and gentle and his courage comes and goes. In one instance where he meets Ankhulfr, a giant wolf, his reaction is "RUN!" Then when he meets Apocalypse for the first time (who makes a show of his entrance with fiery things), he actually takes on more of an aggressive stance.