Book from villians point of view

Hey reddit. I have some time off in the year and looking to write a stort that ive had in my head for years now. The issue is the main character isnt a good person, so was looking for books where the main character is a villian. Not morally Grey, but cold hearted, ruthless villian. Id love to read these books as a reference on how to portray my character to still be relatable while not losing who they are. Thanks