MechaTarrasque
Hero
I thought he used to be beautiful in some of the editions, I mean preslug form. I mean fly face is not a step up from slug form in the looks department.
It was a big part of his lore in 4e: he was a beautiful angel with a propensity for architectural design (surprisingly important fact) who was unhappy with all the gods were not doing to fight the elemental chaos (to be honest a pretty fair assessment); Asmodeus was the exception (short-lived Blood War did occur), but when Assy let the BW wind down, BZB rebelled and temporarily took over the 9 Hells; but when Assy took over again, he turned BZB into a giant maggot, and although he still ruled his section of Hell, it was cursed with rot and decay, which meant all his architectural creations all falling down as fast as his damned minions can build them again. It was intimated that he is now quite insane (but that hasn't interfered with his duties).
I have no idea how much of that made it into 5e (or MToF).