Ex-military hero books have been popular since World War II and have remained popular since then. The main character of these novels is usually an ex-military officer who has been discharged from the military due to injury or some other reason and now works as a civilian doing something else.
Ex-military hero books can spin off in many different directions. Some read more like biographies, but many more are romance novels about women who love ex-military men who are brave and strong but also damaged in some way. often the woman is the only person who can reach the troubled vet.
Other ex-military hero variations include books where a team of ex-military men and women work together for a common goal back in civilian life. These books can be mysteries, thrillers, urban fantasy, science fiction or action adventure.