EVEN A HERO NEEDS A MENTOR
The mentor is arguably the most important figure in the story. Without him, the hero cannot learn what he needs to know to win the battle, save the universe or rescue the damsel. Obi-wan, Mr. Miyagi, or John Keating from the movie Dead Poets Society, each of these characters casts their shadow over the world they were a part of. Even the Kurt Dussander, former nazi from the Stephen King story, Apt Pupil is what the main character needs to fulfill his role in the story. Teachers are the most important job in society and they have a special place in literature.
And so it is for Suma, the wizard assigned by an race known as the Ancients to guide David through his quest and act as his teacher. And like all people he has a past and secrets he has to hide. Suma is uniquely qualified to understand and help his student in his quest. He knows Draga as no one else alive can, he is his brother. It is this association and special knowledge that makes him so important to David's quest and although he knows he has to do this, he knows that he is being asked to help destroy his own brother. He still loves the brother he had, he cannot save the being his brother has become.
I had many good a teachers in my life and a drew from them as well as those I'd seen in books and movies. I used my experience in the martial arts, both as a student and as an instructor to give Suma's teachings a slightly Asian touch. Ultimately, the students no longer needs the mentor and so the mentor moves on, sometimes tragically, and other times to teach others. Yoda dies, and as Nanny McPhee puts it, "There is something you should understand about the way I work. When you need me but do not want me, then I must stay. When you want me but no longer need me, then I have to go. It's rather sad, really, but there it is."