Who is Derek Holtzer from The River and what is their importance?

Derek Holtzer is a psychologist. He works for a government school that teaches survival. Never having had to survive in the wilderness, Derek is selected to go with Brian when he returns to the wilderness because it is the psychological aspects of the experience that the school is most interested in.

Derek is ill prepared for the experience, but he follows Brian's every action...... the trip is surprisingly pleasant. When a freak thunderstorm comes, however, Derek is struck by a lightning bolt and left in a coma. It is up to Brian to save Derek's life.