Jake Mercer is an agent with the American Secret Service.
This is an agent (okay, Jake knows that it is officially 'special agent' but he does not get upset when folks [usually] omit to annoy him]) who has the often thankless job of risking his life every shift protecting the Chief Executive.
Normally I would not have an entry in this compendium for such a position, as important and honorable and dangerous as it truly is, but I make an exception for Mercer because the number of enemies that Mercer will be forced to go up against are often terrorists, some foreign and some domestic, who have even greater unpleasant objectives in mind than just the demise of one individual.
The American President is a magnet for homicidal miscreants and Mercer seems to be perpetually in the right place at the wrong time which is lucky for the nation's leader because Mercer is also a very capable and dedicated operative who would rather die than fail and he has no plans for either. We are told at "He ran a little hotter than most agents, although usually, he was able to keep that heat under control."
Mercer has been in the Service for some time when we first meet him and the current sitting President, Bryan Jackson, is not Mercer's first protectee. He will become very important to Mercer over time, not only through mutual respect and friendship but because of the President's grown daughter, Sheila, who will quickly become extremely important to Mercer.
Also playing a very important part in these adventures is the young but still extremely capable Jess Foster, Mercer's partner in the field. Foster and Mercer make a terrific team even though they are drastically different types of people. While Mercer is intense and quick to annoy - and willing to show his annoyance - Foster was described as "young, bubbly and almost painfully optimistic". More important, to me, though, was that, as we are told in the first adventure, one of her "many valuable qualities was her connection to nearly every agency in D.C. and the surrounding areas". This constant "knowing a guy" will help many times over.