Tom Gray is a security consultant.
As the series begins, he is the founder and owner of Viking Security Services, a very successful organization specializing in providing bodyguards to companies whose business takes them into hazardous regions. Of late his primary region of operation has been the Gulf states in the Middle East but he can and does operate elsewhere.
He had started the company soon after leaving the British Army. In the five years it has been in existance, Viking has worked to largely provide advisors who look for weaknesses in a security system and provide training in shoring up those deficiencies. Viking has a small cadre of full-time employees but has a roster of over a hundred freelance operatives available when needed. Determined to only hire the best and most reliable men and women, their competence reflected well on Viking and Tom Gray personally. As a result, business was good and profits were respectable.
That would come into bearing when, in the opening pages of the first recorded adventure, Tom Gray's personal life is destroyed by a career criminal. It was horrendous to lose his loved ones but when the thug gets an incredibly light sentence, Gray decides his expertise can be used for things other than just guarding someone - knowing how to stop a very bad thing from happening means one has to know how to do the bad things, and Tom Gray is very good. Note to the readers, though, his approaches are definitely "outside the box".
As the series progresses, his "career" will take some definite changes but his abilities will always be needed and he will not shirk from the call. His identity will be forcibly changed for a while to Sam Grant but he stays as good as ever.