My McAnally Theory
Pretty sure it's been suggested that Mac is >!one of the Grigori, or Watchers. An angel that fell and fathered the Nephilim with human women in the book of Genesis. !<
For anyone that hasn't heard this theory, >!it's based on the interaction Dresden has with Mac when he tries to look at our mysterious bar-keep with the sight. The last being to stop Harry from looking at them with the sight was the Angel security guard in Ghost Story. So, I think it's safe to assume Mac is some kind of angel. Shark-face also calls Mac "watcher" in Cold Days and hints at a decision "made long ago". !<
My theory is that Mac is specifically >!Penemue (https://en.wikipedia.org/wiki/Penemue) from the book of Enoch. Penemue taught "the children of men bitterness and sweetness", like the ale Mac is famous for. Penemue also taught mankind how to write and make paper, allowing them to record knowledge for future generations. So, if Mac is Penemue, then maybe he's also connected to The Archive in some way? Much later, of course. I'm not suggesting The Archive is antediluvian. !<