Nathan 'Nate' Hendrix is a former agent with the CIA.
When we first meet him, in a flashback five years to an operation in West Africa, he is leading a fair sized team of paramilitary operatives taking out a mercenary-led militia belonging to a very nasty mining corporation. A key takeaway from this adventure is a statement that "His tattered clothing and mud-encrusted boots were as worn out as he was from years of jungle living"; Hendrix has been doing this sort of work for a long time and that weighs on a person.
Returning to the present time, we find Hendrix living a very peaceful and enjoyable life in Blayne, Utah, just northwest of Four Corners, under the name of Nick Mercer. His line of work has changed dramatically to that of a furniture craftsman; he is admiring a custom kitchen table when we start following him. As it sounds, his life is mundane and fairly serene, a far cry from the hellishness of his work for the Agency and something far better suited for his psyche.
Unfortunately, when he was doing the missions in years before, he had made a fair number of enemies who still harbor considerably bad feelings towards him and, when a leak occurs revealing his new identity and location, his peaceful world comes to an abrupt end and Mercer has to return to being Hendrix which is unfortunate for him and decidedly unpleasant for those coming after him.
In truth, though, it is pretty obvious that Hendrix, despite the truly felt desire for a peaceful existence, is a man of action which is a very good thing because as we discover following him, wherever he goes, there seems to be trouble that needs handling and Hendrix is very adept at handling it, which makes it no wonder that some folks at Langley who know just how good Hendrix is, keep tabs on him for those occasions when someone like him is needed.