Joshua McCord is an agent for the President.
This position is an unofficial one in that as far as the world is concerned, his actions do not exist and he is not connected to the White House in any capacity but in truth he is the go-to guy when the President has an especially difficult job to be done. We learn fairly early on that every Chief Executive since Abraham Lincoln has had at his covert disposal a highly trained and extremely capable operative to be on call and be a "person he can count on for whatever needs to be taken care of" - "within the bounds of reason and morality". "The position is highly classified. The fact that it even exists to known to very few."
When we first meet McCord, he is nearing the end of his career as the current agent. On a vital mission for the President, he realizes that his reflexes are not as they once were and since things are not going to get better, he seeks the advice of the man that he had replaced years before. That advice was that his new primary goal must be to find a suitable replacement and to train the new guy (or gal) to be what it means to do whatever he is called upon to do.
When McCord is not on a mission for the President, he has a day job as a professor at Dedman University (interesting choice of school). While his exact area of academic teaching is not mentioned, he is shown to be giving a lesson on the Japanese code of Bushido, complete with a very impressive demonstration with a katana. Naturally, when the call comes from the Oval Office, he drops whatever he is doing and responds.
Acting as the buffer between the President and his covert agent is a young woman named Que who demonstrates several times that she can more than hold her own in combat, probably because she is also McCord's daughter.