Ray Guinness is an agent with the CIA.
Guinness had been an assassin working for MI-6 for many years until he had grown tired of the killing and wanted out. Getting out, though, was always dangerous because old enemies and your former friends all feared what you might do or say but for five years he was able to hide out in the northwest of America, married to a nice, plain, undemanding woman. Then someone killed her and he was pulled back to his old life. At first he was saddened at the loss. Then he was angry at attack. Then he decided that pulling him back in should be a mistake that someone paid as dearly for as his wife.
Though Guinness had been an agent for MI-6, he was an American born and raised. He grew up in Ohio and, though fairly poor, managed to get a scholarship to Ohio State. He wanted something more, something different, and reading through a list of schools decided that a time at the University of London was what he needed. This meant working a full time job while getting his degree but eventually he had what he thought was enough money to head to England. Things didn't go as he had expected. He got into their graduate program but without a work permit, he couldn't eat. That was when MI-6 came calling. An American student would make a great cover for a British assassin. They offered and he accepted. And stayed long after his schooling was done.
When he quit, he knew they might come after him and they did. Now that he was returning to his old profession, though, he realized he had no desire to return to England and the CIA had been there to help out so he offered his services to them. He is still tired of the killing and tired of the pressure and the anxiety living on the edge constantly presents. He is just very good at it.