1) Unfamilliar with that movie. But basically - someone who can't really be let out back into civilian life due to being for most intents a highly functioning psychopath. He's rational, he doesn't have any weird urges, and he won't find shooting children or cutting off his own leg crushed under the rubble any harder mentally than smashing eggs to make a breakfast. Neither he would flinch under the heavy machinegun fire - fear for his life is more of an intellectual concept to this guy. He doesn't get bored, does not doubt his choices(merele acknowledging badly made ones) and is physically incapable of getting angry. He's a perfect soldier, mental integrity-wise, but that also makes soldiering and similar high-stress professions the only thing he's good for.

2) He's probably former special forces, volunteering for the procedure.