Alex Boyd is an agent with the DSS.
Technically he is a Regional Security Officer, not an agent, as he works for the U.S. Diplomatic Security Service, and as such he is "the principal security attache and advisor to the U.S. Ambassador at American embassies and consulates (Wikipedia)". According to the State Department's website, there are several important tasks assigned to the RSO including serving as the embassy's law enforcement liaison with the host nation but protecting the diplomatic facility and its personnel is by far the most important and tasking.
Our initial meeting with Boyd is when he is the number two man in the RSO office in Islamabad, Pakistan, and is about to be forced to prove how good he can be when the U.S. political scene decides it is more important to take the side of India over that of its arch-rival. It is the late 80s and tension between the two nuclear powers on the Indian subcontinent is as taut as it has been in years. Boyd will be forced to do things his way when the choice between strictly following orders from a Washington which has no real grasp of what it is like in country, or doing what it really takes to keep his charges alive.
Amusingly, when he is moved to Rome as a reward during the second recorded adventure, he will find that life in a "tame" environment like Italy can have some major problems as well and will require a different approach, though it will still call for a lot of action and putting his life at risk yet again.
Boyd is 35 years old when we join up and has been with the State Department for several years. He is single but 'looking'. He is 6'2" in height and makes sure he stays in the best physical condition he can because he knows that his life really does depend on it.