Sam Capra is an agent with the CIA.
At least he is for the first few pages of the first novel and after that he is a prisoner of the Agency and then a fugitive from the Agency and finally someone the Agency might forgive but never fully trust. Most of that is explained in the beginning and does not count as a spoiler.
Described by a couple of characters in the books as in his mid-20's, Capra probably fits better as being late 20-ish considering that he has been an agent with the CIA for several years before marrying Lucy and they were married for three years before the start of the series. He is definitely a man whose career is on the rise, confident though not cocky, and excited about what he has done and is likely to continue to do with his work.
For relaxation, Capra is an avid participant in parkour, the relatively new form of exercise training that involves gymnastic leaps and bounds against objects and over obstacles, much as a monkey might be seen doing in the jungle. Little wonder one of the major characters in Capra's life would start to call him that affectionately. When the series opens, he did it as a way to stay in shape for his next assignment. After his life falls apart, he does so as a coping mechanism.
Fall apart is an understatement. Moving up the chain in the Agency with a beautiful wife who was eight months pregnant with their first child, Capra was enjoying an almost perfect life. Then a frantic phone call from his wife draws him out of his office building only to see her abducted. He gives chase to no avail. Then the building he was just in explodes, killing all his workmates. With his wife gone, he the only survivor with no proof as to why he was not killed, Capra is the chief suspect and the CIA is not known for gentle interrogations. From perfect to disastorous in a second.
As the series progresses, Capra is faced with more questions then answers. Who is in the group Novem Soles? Is the CIA after them or helping them? Who is the beautiful and enigmatic Mila who saves his life several times. Who are the people in the group The Round Table and are they his benefactors or just as bad as the others. Important questions but nothing like the ones plaguing him the most: where is his wife? where is his son?