Neal Stephenson and "cameos"

Okay, I admit it: I am a Neal Stephenson geek.

However, so are, inter alii, law professors Eugene Volokh (of UCLA law school and the excellent Volokh Conspiracy blog) and Larry Ribstein, of UIUC law school (see his blog entry on Cryptonomicon, which he calls "the greatest sci fi book ever.") Professor Volokh has made numerous references to Stephenson in the Conspiracy.

At one point, Professor Volokh writes, "Which character in Cryptonomicon is likely a descendant of Eliza, the Quicksilver/The Confusion [and presumably, The System of the World -- available September 21] character?

The answer, of course, is German mathematician (and Alan Turing's lover) Rudy von Hacklheber. I unfortunately first read his trivia question through an RSS aggregator, which did not properly hide the answer to the question (as he had intended).

Anyway, I have a Stephenson trivia question I am proposing to Professor Volokh, and to you all (ha, ha) here: I was re-reading some Neal Stephenson recently when I noticed that there is actually one (major) character who (almost certainly) appears in two of his novels. The second reference is small but significant, but the reference is not passed by name, as it were, but by description. Does anyone know who it is?

Please email me the answer at mitchell (at) silverman-esquire.com. (Yes, this is me.) I have some hints I'll be posting if I don't get any answers.