Mark
CreativeMountainGames.com
I've been wondering for a while if it's just me that don't assume Orcus, Demogorgon and dudes like them as the "ultimate evil".
They are in the cover of the last two monster manuals, fairly common ground these days. Every player meta-know who they are: Orcus, Demogorgon, Baphomet, Dispater, Graz'zt, etc. There's no surprise, no mistery and that don't work very well for me.
So, in my games there's always something hidden, strong, fierce... creatures, or maybe the essence of evil, that represents a mistery even for the archdevils, taunting them, whispering mad secrets... infusing them with power.
What about your experience? Are your games straight to the MM devils and demons or there's something different around?
I like to go the opposite direction. I have found that the best villains are those that would not normally arouse suspicion.