What was Roger Chillingworth's change of character in the Scarlet Letter?

I have to write an essay about Roger Chillingworth and how he changed as a character from the beginning of the book to the end. The thesis statement I must complete is "In the Scarlet Letter, Nathaniel Hawthorne's Roger Chillingworth begins as ______________ but evolves into __________. I need help filling in the blanks with his character change. Mainly how he first acted and then his change into being a revenge obsessed monster. If you could also include a part of the story that supports your opinion it would be greatly appreciated. Thank you