William 'Mack' McLendon is an agent with the CIA.
As the two-book series written by a long-time employee of the Agency begins, McLendon is semi-retired from his job where he had worked for nearly three decades, dating back to the time of its predecessor, the OSS. Since he left, he has been using his law degree earned many, many years before, to keep himself busy although he deals mainly in wills and such. As he tells the people who come calling on him looking for someone with his experience to help out, his pension from the Agency is enough to keep him comfortable and he works in an office as an attorney more for something to do than to earn a living. This dislike of inactivity likely was the chief driver for his returning to the fold, albeit on an informal basis.
McLendon's departure from the Agency was not as totally amicable as it might have been though details are not forthcoming but it was only with certain people at the top and those people are long gone, leaving the stories of the best counter-terrorism agent that ever worked there intact. Nicknamed Mack the Knife by those who regale recruits with stories of derring-do and actions often bordering on the fantastic, his exploits still resonate well and make him the perfect candidate to approach when a top Agency-trained operative was needed but the Agency could not get involved due to political reasons.
The first book in the series recounts the incident in which McLendon is pulled back from retirement to go after the infamous Carlos the Jackal, although evidence indicates that the original Carlos was dead and his role now played by a former CIA agent who was even deadlier than the real thing. It is McLendon's job, hired by major businessmen under the unofficial auspices of the Agency, to go after Carlos and put him down one way or the other.
The second book, taking place a decade later, has a McLendon in his mid 60's asked once again to help when the fake Carlos, having created a small cadre of skilled assassins, escapes from prison and needs to be ended for good. While McLendon is not the main active agent is this second adventure, he plays a major and critical role.