The Art of War, written by Sun Tzu in the 5th century, is so much more than a military strategy book. This book has been used by people to help with business tactics, legal strategy and even for making lifestyle choices!
The text is about how to outsmart your opponent without having to engage in battle - so it's oddly relevant to modern day life. The Art of War is often referenced in mainstream TV and film, so reading it will also help you better understand inside jokes and references in popular media.
Click the link to grab your free copy of a translation by Lionel Giles.