He's an army brat turned military police veteran, who basically ditches possessions and wanders America with a bare minimum of material goods, but he keeps on encountering mysteries and criminal conspiracies and whatnot. He's a huge guy with really great situational awareness and fighting skills, and was a crack investigator in the military and is way more intelligent and well-educated than his brutish appearance indicates, so he is surprising effective at solving these mysteries and giving out necessary beatdowns and hooking up with a female LEO or peripherally involved strong woman.

They made a couple of movies based on the books, starring Tom Cruise, which offended many people, since Cruise is well short of Reacher's size and physical presence. And Moiraine was in the first one.