Mr. Griffin
The eponymous Mr. Griffin is a high school English teacher who demands the world of his students. He doesn't allow his students to turn in late homework and doesn't take any excuses. He is a perfectionist and doesn't particularly care about how popular is with other people - but particularly his students.
Mr. Griffin, however, truly cares for his students and wants to see them grow and succeed as writers and as adults.
Susan McConnell
Susan is one of Mr. Griffin's students. Intelligent but lonely and naive, Susan dreams of being popular and being widely accepted in high school but has thus far not been able to achieve either. Susan, along with a number of other people in Mr. Griffin's class, is chiefly responsible for Mr. Griffin's kidnapping and ultimately, his death. But she quickly becomes aware that what they have done with Mr. Griffin is wrong and that everyone should feel badly about their actions.
Mark Kinney
On the surface, Mark appears to be an oblivious student who lacks a modicum of intelligence. Mark, however, is an incredibly intelligent and all-seeing person who is able to pinpoint someone's weakness and exploit that weakness to achieve what he wants. He is incredibly manipulative and vengeful and was one of the leading forces in kidnapping Mr. Griffin.
