Richard Yokely is an agent with Grey Fox.
"No one knows for sure who Richard Yokely worked for in the past - the Army, the CIA, DEA, NSA - he has carried out missions for them all. But now he works for Grey Fox, the super secret agency that takes care of business that the White House would prefer to keep under wraps."
More to the point on this organization, and its best operative, "Grey Fox was the agency that the President turned to when he had problems that the conventional agencies were unable to deal with. Often those problems could only be resolved by assassination, something that Grey Fox operatives were skilled at. In years past, Yokely would be briefed by the President or the Vice President, often in the White House itself. He had met every president from Ronald Reagan to Barack Obama and had carried out missions for them all. But the current incumbent of the White House had not been told of the existence of Grey Fox, partly over fears that he might mention it during one of his regular late-night Twitter sessions, but also because of the genuine risk that he would want to use the agency for his own ends."
We do not learn much about that organization beyond the statement above. One important fact that is made known to us is that Senator Rex Adams, a 70-some year old politician with considerable influence on Capitol Hill and one nicknamed "the black J. Edgar" because "he was widely believed - with good reason - to have dirt on just about every politician in Congress" and the current chair of the National Security Committee, "was also the link between the White House and the Grey Fox group." Adams has a very long and close relationship with Yokely.
As Adams mentions in secret once, "There were as many versions of Richard Yokely's back-story as there were people recounting it, but there were two things that everyone agreed on. Yokely was undoubtedly the best of the best, relentless in pursuit of the task, and an emotionless professional killer as adept with a knife or his bare hands as he was with weapons and explosives. However he was also a dangerous man to get on the wrong side of, because he was an implacable enemy of anyone who dared to cross him, willing to nurse a grudge for as long as it took to get his revenge".