Jake Noble is an agent with the CIA.
He has been for a good amount of time when we first meet him and in his mind the mission he is starting during that adventure was just another one, not knowing that an unfortunate twist of events would make it his last assignment for them. For a while at least. Then their need for someone with his skill set will bring them to him and family financial needs will get him to return. During that break in time, which will last four years, he will earn a living as an underwater photographer.
But Noble knows his true abilities lay in saving people. Finding them wherever the people doing the snatching have stashed them and getting them back. Simply put, his "job was to eliminate bad guys and rescue hostages". He was good at it and he enjoyed it. He tried hard to not be too bitter about his forced separation from his job. He was ready to come back when they asked, and they did ask.
Noble is described as "lean and hard with tan skin and shaggy hair, he looked ... like a surfer". He is likely in his early to mid 30's having been with the Agency for several years and a member of the Green Berets with several tours in Iraq and Afghanistan before that. He was seasoned and experienced and darn good at his job.