Mouseferatu said:
I've heard that, and I know
some of what happened. But if you don't mind taking a moment, and if the other good folks don't mind a brief hijack, could I impose on you to sum up his story for me? I know he's not the Oinodaemon anymore (Boo! Hiss!), which is something I plan to rectify if I'm ever permitted to work on anything official involving him.

But I don't know what lead up to that, or much about his successor, or what he's doing now (other than wandering around looking for his staff, or something, right?).
Essentially Anthraxus is currently wandering the lower planes of conflict (Gehenna, the Waste, Carceri), offering his services to various deities in exchange for being installed as a proxy of theirs, with the deific granted power that would entail. However, as of the moment, no deity has taken him up on the offer given his nature as a 'loth. Presumably he still has the Staff of the Lower Planes, because it isn't mentioned that he lost it, or that Mydianchlarus has it instead. It was more something Anthraxus had, rather than being a sign of position atop the Seige Malicious of Khin-Oin.
As for how Anthraxus lost his position as Oinoloth:
Mydianchlarus, a massively powerful Ultroloth, is said to have whispered a secret into the ear of Anthraxus that was so profound in its implications that Anthraxus simply ambdicated his/her/its position as Oinoloth. Mydianchlarus of course happily filled the position atop Khin-Oin, and personally I like having an Ultroloth there, rather than one of the so-called 'Altraloths' who are semi-independant from the standard 'loth heirarchy (see Ed Bonny's very nifty article in Dragon Annual #1 [IIRC]). Yes, this screams plot hook for any DM. Either the secret could be whatever you want it to be, or it could have been a complete and utter lie (which is ever so fitting for the 'loths).
Personally I went all out on this in my 1st storyhour, delving into Anthraxus' position after he was deposed, and ultimately his conquest to retake that position. Of course it ended badly for all involved, and I ended up killing off both Anthraxus and Mydianchlarus both in the course of the plot. I also explored Anthraxus' motivations, Mydianchlarus' and the secret he told to his predecessor, and also setting up what happened before those events
right here in one of the Baernaloth cycle stories of mine.
I had fun with the unique 'loths as both singularly potent individuals, but ultimately puppets of their creators, beholden to them in ways that they loathed at the same time they felt a near religious devotion to them.