The Teeth of the Tiger, by Tom Clancy.
Clancy introduces John (Jack) Ryan Jr., and Jack's cousins, fraternal twins Brian and Dominic Caruso. The three work for "The Campus," a deep black undercover organization tasked with the job of tracking down and eliminating threats to the United States by any means necessary, including assassination.
Rainbow Six, by Tom Clancy.
John Clark, Jack Ryan's sidekick, is the star of this massive techno-thriller as he takes control of an international anti-terrorist organization. The team's first order of business - save the human race!