Patriot Games/Nightmare Fuel


 * Sean Miller is In-Universe nightmare fuel for Jack Ryan. From the first time they meet face to face, it's obvious Miller wants Jack dead, and his first actual words on Ryan admit as much. Miller targets his family, and the ULA he works with makes an explicit point of using his own planned death (which Jack barely avoids thanks to the assassin being intercepted) to advance their agenda, and then towards the end of the book they plan to finish what they started earlier. For Ryan, Miller and all that supports him are a very real fear that he only gets to rid himself of at the very end.
 * In fact, this actually gets flipped around at the very end. Miller has been a remorseless murderer while Jack has tried to retain his humanity, but by the end of the book, RYAN becomes MILLER'S In-Universe nightmare fuel because Ryan manages to corner him and almost kills Miller with a point blank pistol shot in the mouth, and as Ryan is pulling the trigger, Miller is the one who now knows the terror he's made Ryan feel the whole book.
 * The aftermath then passes the nightmare fuel back to Jack, as even though he DOESN'T kill Miller, he remembers since that moment he almost became the very animal Miller had been, though the scary part of this proves a long term good thing, as it reaffirms to Jack Ryan that the rule of law is a far greater and more honorable punishment for people like Miller than attempting to Pay Evil Unto Evil.