Xander King is a freelance agent.
Sort of. He works for himself, on missions he feels he should go on, when he feels the time is right to go on them. No one can really dictate what he does. In that regard, he is a freelancer because he is independent. The iffy part is whether is it proper to regard him as an agent as opposed to an adventurer. I opted for the former but the matter is open to debate.
To the world, according to one description, Xander, short for Alexander, is "a handsome, charismatic, and successful young businessman who was able to rise above a violent tragedy in his past". That tragedy was the murder of his parents more than a decade before. The public knew, as much as they ever could know, that he had inherited control of his father's oil business and was now, along with his younger sister, extremely wealthy. It was also known that he enjoyed a very pleasant life style living in a gorgeous Kentucky mansion on his thousand-acre horse farm, being involved in numerous charities as well as owning a championship race horse that he doted on.
Not a bad life all said.
The CIA, and other intelligence agencies around the world, know a totally different Xander King. This one was a man determined to get justice for his parents so rather than go to work at the oil company, he chose to sell it and to acquire fighting skills and hone them by joining the military. The Navy, to be exact. And then to become one of the elite SEALs. The combat skills learned there were exactly what he wanted and he soaked in everything they had to teach.
After his time with the SEALs came to an end, he started his real occupation - seeking out who had murdered his parents to make them pay. And in the meantime, he found a fair number of other extreme low-life's who had done horrific things and managed to elude justice. King brought it to them as judge and jury and executioner all in one.
Along the way, King had come across Samantha Harrison, an MI6 operative he became friends with and when she grew tired of the bureaucracy of her organization, she left it to become King's partner in whatever you might choose to call what they do.
The CIA learned about this activity and instead of feeling it necessary to stop him, the Director opted to do whatever it took to get such a splendid killing machine on his staff.
The thing about being a fierce warrior with seemingly unlimited resources is that no one can really make you do something you do not want. You can, and the CIA learns, ask nicely and hope for the best.