Shaw is a killer for a unnamed secret International Intelligence agency.
An orphan when abandoned by his mother at age two, Shaw has no recorded first name. He took the letter A as his first initial only because it happened to be above his bed at the orphanage and it was better than nothing. He never bothered to put a name to it.
For several years he worked as a freelance agent for whichever Western power needed him. Then an encounter with Frank Wells, who thought Shaw might be working for the other side, went badly for both of them. Wells tried to have Shaw killed but ended shot in the head, nearly dying. Shaw saved Wells' life but was rewarded with a promise of many years in prison unless he worked for the agency.
As the series opens, Shaw is ready to retire. He had been told when he first started that his servitude would last five years. He had already worked six years before the first book and felt that was more than enough. Wells's superiors did not agree. Even as they moved towards an unpleasant impasse, the trouble documented in the first novel put them on the same side again, albeit without any warmth.
Shaw is, according to Wells, the best he had ever seen in the business. Practically fearless, he knows how to get out of most impossible situations and for those he doesn't know, he improvises. Shaw believes, however, that he is so good partially because he no longer cares what happens to him.
Even the threats of what would happen to him should he quit without permission did not faze him except for his immense dislike for being pushed around. He had had enough of that as a child in the orphanage. As an adult capable of killing in dozens of different ways, it was not going to happen.