Professor Minerva McGonagall
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Professor McGonagall teaches Transfiguration; she is also Head of Gryffindor House. She's a no-nonsense individual with a strong sense of duty. There are plenty of indications in Book 2 that Professor McGonagall is following in Professor Dumbledore's great footsteps. She takes over as temporary Head of Hogwarts after Professor Dumbledore is dismissed by the school governors. She, like Professor Dumbledore, teaches Transfiguration (a small detail about Dumbledore revealed by Tom Riddle). Professor McGonagall is a solid, dependable presence at Hogwarts, even if she doesn't have Professor Dumbledore's charisma or depth of power. Also, she does her best to reach out to Harry and Ron once Hermione is Petrified and Ginny is taken into the Chamber of Secrets.