Harper Collins calls the book:
An unstoppable collection of the most hardcore figures who ever strapped on chain mail and ran screaming into battle
And from what I saw while skimming through it last night, they are right. Ben Thompson's Badass tells the story of badasses like Chandragupta Maurya, Wolf the Quarrelsome, and Bass Reeves. Don't know who they are? Read the book.
In addition to being a collection of badasses, the book also has a sections of badass-related topics such as "The French Foreign Legion" and "The Ten Least Baddasses in History."