Foreign intelligence agencies take people who tend to agree with their positions on at least one significant issue, such as opposition to some element of a nation's foreign policy, and then seeks ways to motivate and help that person become a successful advocate on that issue within their own circle of influence.
The ultimate prize of an intelligence agency is to have someone sympathetic to their own goals and ambitions in a position of power in an opposing organisation or country.
In 1980, Ian Adams uncovered evidence that John Watkins died while being tortured by the Royal Canadian Mounted Police and the United States Central Intelligence Agency in a failed attempt to get him to confess to being an agent of influence. In 1999, Adams wrote a novel Agent of Influence, based on the event. This was made into a 2002 Canadian movie of the same name.