Samuel Carver

Samuel Carver, a former British marine, now a hitman who arranges accidents for bad guys around the world.

Samuel Carver is an agent with MI-6.

To be more accurate, he is an agent during the latter books in the series. At its start, he is an independent assassin. He is called the Accident Man because his speciality in killing is to make it look like an accident, so real that even on the closest of examinations, the proof that it was otherwise is not there. Some people might suspect otherwise but proving it was not possible.