Jack Ryan, jr. is an agent with The Campus.
Ryan is the second child of and Cathy Ryan, one of four children. As his father rose in rank with the CIA, Jack jr. enjoyed a normal middle-class upbringing, eventually going to St. Matthews Academy and later Georgetown University as his father had. He majored in History and had an eye towards teaching but situations later would change that path. When his father became President, he tried to remain as far from the limelight as possible though he was forced on occassion to mingle with head of state and other major dignitaries.
When terrorist activities became such a constant threat, Jack decided his life of safe academia was not the way he should go. He wanted to use is extremely intuitive mind in the fight against the enemies of his country and he chose to approach The Campus for that opportunity. Initially he intended to work as an analyst, much as his father had in his earlier days in the Agency. Events taking place during his first major assignment, though, put him squarely in the action and his role had to change to survive.
The Campus for which Jack works is officially known as Hendley Associates, a "financial trading company" as far as the majority of the world knows. In fact it is a secret anti-terrorist organization which President Ryan established during his closing days in office. Under the direction of former senator Gerry Hendley, the Campus lies roughly between the workings of the CIA and those of its sister organization, the NSA. It is totally off the books and pays its expenses through "stock market trades influenced by the captured intelligence data" (according to Tom Clancy's wiki).
Working with Jack at the Campus are his twin cousins, Brian and Dominic Caurso. They were the two who, seeing that Jack was no more likely to stay out of the action than his father had been years before, took it upon themselves to help train Jack in fighting both hand-to-hand and with weapons. Brian was a former Special Forces soldier while Dominic had been a highly experienced FBI agent before they both joined the Campus.
Also employed by this mysterious unofficial intelligence group are John Clark and Domingo Chavez. Clark's decades of work as a covert CIA operative, often with or against Jack sr., and his time with Chavez as part of Rainbow Six, provides the Campus with the benifits of a lot of learning the hard way.
The books that make up the Jack Ryan, jr. series are a continuation of the series but they deserve their own distinction because the emphasis of the storylines are on the son, not the father. Since the father plays a role, though, the books also fall into his listing as well.