Here are the following connections to Theory and Mathematics that surprised me (and would surprise my mathematics teachers . . .)

Erdos Number: The Erdos number of a mathematician is a measure of the "collaboration distance" from the noted discrete mathematician Paul Erdos. Erdos himself, one presumes, has Erdos number 0. People that have co-authored papers with him have Erdos number 1. My Erdos number is 2 via a paper I co-authored with Ron and Fan Graham.

Acaademic Lineage: In a similar tradition, mathematicians and theoretical computer scientists often trace their family tree with their advisor as their parent, their advisor's advisor as their grandparent, etc.

The Mathematics Genealogy Project traces my lineage via Nancy Lynch to Hartley Rogers, Alonzo Church, Oswald Veblen, E.H. Moore, Simeon Poisson, and Joseph Lagrange. They go even further and with some fudging (since Lagrange never wrote a thesis) to Euler, the Bernoullis, and finally to Leibniz himself.