I'm looking for books on Clical Musicians?

I just recently got into clical music guys like Bach, Mahler, Beethoven, Chopin, Brahms, and Mozart. I love the sound of their music, it is really beautiful and peaceful and sounds meaningful. However, I feel like if I knew more about these guys then I would better understand their music. Are there any good books out there that would help to expand my knowledge on these artists and their music.