Devlin Stone is an agent with Z Section.
That is a division of a bigger company called Eagle Alliance, "a San Diego-based paramilitary company that had exclusive contracts with the U.S. government". Z Section is a "secret department of the Alliance that had a different kind of relationship with the U.S. government as well as other Western powers in that it handled the covert operations that those governments did not want to handle."
We get an introductory look at a 16-year-old Stone, happening 20 years before, when the building in which he and his family were living was engulfed in flames and everyone but he perished. As he watched in shock at the destruction, a man "dressed head-to-toe in black" and wearing a silver ring "with an eagle's head carved into the flat top" told him that Stone had to go with the man because others would come looking for survivors, people who would see to it that there were none.
Those coming were members of a drug cartel and they had a particularly heavy axe to grind with Stone's father but nothing like the vengeance that Stone would be seeking years later, after he had spent most of his adult life becoming an especially sharp and lethal fighting weapon.
The man doing the rescuing was Brad Preston and he would be the man who not only saw that Stone survived that horrible night but also found his way many years later to become part of Eagle Alliance. In the present it is Preston who gives the orders that send Stone to various parts of the world, constantly putting his life in danger.
Two short comments in the first adventure say a lot about Stone. The first was that he "didn't look like a killer". The second is that he "had a talent for killing bad guys". He would use the former to get close enough to targets to do the latter.