Um, make that a non-obvious reappearance

Um. Guess I'm not the Stephenson geek I thought I was.

As the estimable Professor Volokh reminds me, Enoch Root, who first appears in Cryptonomicon, also appears in Quicksilver and The Confusion (and, one presumes again, in The System of the World).

So allow me to be more specific: the reappearance I am thinking of is non-obvious, and the character does not have the same name. Further, the reappearance I am thinking of is in exactly two (no more, no less) of Neal Stephenson's books.

Of course, anyone who comes up with another instance that meets all my criteria will be pummeled brutally with a copy of The Big U warmly congratulated and have their answer also posted here.

¿Está claro? Muy bien.