Mr. Petrachelli was one of the teachers at Bayside High School.
He is a universally hated teacher who would rather torment his students than teach them. He deliberately asks questions only to students who do not have their hands raised and ignores those that do. He also has a disgusting neck crack.
He has "Terminator"-like vision that not only helps him find students who do not know the answer, but also confirms that he really does enjoy tormenting his students rather than teaching them. He would usually label students who know the answers as 'Know-it-alls', and students who do not know the answers as 'dead meat'.
Because of one of her visions, Raven talked back to Petrachelli, causing her to get in trouble. When Petrachelli requested a parent-teacher conference, Raven disguised herself as her mother to get out of telling her parents.
Later, Petrachelli missed school for his second job as the mall Santa, where he saw Raven, Eddie, and Chelsea skipping school. Luckily, Raven was found by someone else and the events of the episode were erased.