Code Archaeologist

Definitions

Someone who spends significant time digging through old code, comments, and commit history to figure out why a system behaves the way it does. In engineering slang, the code archaeologist is often the only person willing to study the ruins instead of demanding a rewrite.
In plain English: Someone who digs through old code and history to understand a system.
Example: "She turned into a code archaeologist for the billing service, tracing a weird tax rule through nine years of migrations and commit messages."