Paul Fox is an agent for the Department Of National Defence.
For almost a decade, Fox worked for the Organization, an unnamed section inside the Department of National Defence. When his wife was killed by a Soviet agent as retaliation, he went on a short revenge spree, killing as many of them as he could find, starting with the junior agent who had pulled the trigger. About that man Fox mused once, "...took three weeks to find. He died very slowly...".
What bothered Fox almost as much as his wife's death is that she had never even known what he did for a living, thinking him a businessman who travelled all over the world. It was on one trip that she took with him on a belated honeymoon in France that the killer, thinking she was also an agent, shot and killed her.
After his revenge spree had gone on for a short while, Fox began to realize it was not easing his grief any. So he quit. He quit his vengeance and he quit the Organization. He found a good job in the civilian world actually working as the consulting engineer he had used as a cover, this time for real on assignments all over North America. He finished raising his only child, a daughter, until she was nearing the end of her college and no longer needed her father as much.
As the series starts, he has been a civilian for nine years and was very content with his peaceful, normal life. He had remained a member of the Reserves, however, and it was while training with his military unit that he came upon an obvious act of sabotage in the wilderness of western Canada and did what he was trained to do. He stopped it. And found himself again working for the same people he has left many years before.