Sigmund BrockHans Rotwood's mentor, a researcher of the magical world, and inventor of Brockium - a chemical that will make any disguised dragon revert to its true form - he was a professor at Fumshteiken University when Rotwood was a student there. Brock is brought in to replace Rotwood as Principal of Fillmore Middle School when Jake gets Rotwood fired .
However, because he has Brockium and is determined to catch the dragon at Jake's school, Jake has to get him fired as well. He even resorts to forming an alliance with Rotwood to do so. In the end Brock is fired, and Rotwood is restored to his position as principal.