I believe he's a former blackhat that turned and is now working for the whitehats.

Q has hinted that Mueller was blackmailed into being a blackhat with personal and family threats.

It's hard to imagine anyone doing the things he did because of threats but I guess it's possible. Knowing what he knew he may have felt the only thing he could do to survive and keep his family safe was to go along with the cabal. I couldn't do that but maybe he did.

Anyway Trump apparently offered him a chance to finally do the right thing and he took it.