The Atticus Kodiak series by Greg Rucka follows the adventures and (more importantly) transformation of a ex- U.S. Army soldier turned bodyguard.
The first four books of the series are very well-done but fairly straight-forward thrillers. A few things make them standout among the competition.
For one, the characters are interesting and nicely developed, especially Atticus himself. There's a certain melancholy to him that becomes more and more apparent as the series progresses.
Also, I like the fact that Rucka is not afraid to delve into social issues and get political. This sort of thing can be a big turn-off for many readers, but I think it adds depth and substance. Also, I was a Political & Historical Studies major in college so I might be biased. A word of warning: If you are in the Vince Flynn/Brad Thor/Tom Clancy political camp, Greg Rucka might not be for you.
Then there's Rucka's writing style, which is brisk yet atmospheric.
The fifth book in the series, Critical Space, marks a turning point in the series. While the first four books were essentially bodyguard-based crime novels, from here on the books become something more akin to international thrillers. Many fans were not happy with the changes, but I think the series went from good to great with this book.
While all the Kodiak books are worth reading, this one really stands out from an inspiration standpoint. Atticus Kodiak finds himself on an island in the Caribbean, where he spends months making learning to be one hell of a badass. The chapter in Critical Space detailing his regimen is one of the best of its kind I've ever read. It's sort of like a written version of a training montage from a movie. Essentially, Atticus spends his time strength training (with lots of pull-ups) and practicing martial arts. To aid in balance and recovery, he uses yoga and ballet. (Don't scoff at ballet; it's far more challenging and even dangerous than people realize.) He also goes on long ocean swims. As for diet, Atticus gives up alcohol and caffeine while eating lots of fresh fruit (especially watermelon) and seafood.
By the end of his training, Atticus Finch is essentially a new man. Critical Space is a great example of how a committment to fitness and wellness can lead to something akin to a personal rebirth.