What are some genuinely life-changing books, books that have changed you as a person and greatly impacted you.

I am looking for life-changing book that have greatly impacted you as a person. Books that can make you say that you have genuinely learned something important. I am interested in philosophy, particular ancient philosophy and Ralph Waldo Emerson. Do feel free to post books of a philosophic nature, though they can be fiction/non-fiction/memoirs/pretty much anything etc.