The boy in the striped pajamas.

Herr Liszt is the tutor hired by Bruno's father. He basically gives the lessons in Nazi rhetoric. He goes through all the great stuff the Nazi's were doing! Ethnic cleansing, anti-semitism, German superiority and the swell guy named Hitler were just some the topics on his course outline. Yes he was taking advantage of the children. Bruno and Gretel were a captive audience and impressionable, Gretel took to the lessons while Bruno was skeptical.