In-game and steam Achievement - Neutralizer
Just won with an Ultra with a Neutral character and unlocked "The Grey Hawk" (Become an Avatar of Balance) but based on the description I should also have unlocked "Neutralizer" (Slay the Chaos God in your quest for Balance). I did a search for Neutralizer but didn't see anything so not sure if this is known (it could be that Revered Martyr also does not unlock, but I can confirm that Usurp the throne does).