Probably over half of the replies are voting for Tharazdun. I had not even heard of him until I started this thread.
annnnd this would be where we respectfully ask that you turn in your D&D treehouse membership preferred player card [tm].
But I'm wondering, what is it about Tharazdun that is getting him so much praise? Is there an adventure related to him that is popular and that's what got people so interested in him?
The only feedback I'm getting is, "The gist is that they are crazy evil murderers bent on destroying everything." But I don't see how that makes them all that different or unique from most other cults being used in a D&D game. They don't need to worship Tharazdun to come across like that, so what's the big deal? What am I missing here?
Tharizdun and his worshipers are such a special crazy that even the really bad guys wouldn't worship him and would do anything to kill his cultists. So he has to have cults within cults and often not even the high ranking cultists know what the abyss is going on. A coalition of deities, good and evil, put him down and imprisoned him. In one of my campaigns they also then forgot about him. The main city was nestled within a link in one of the chains, made of mithril and had magical properties. That nation city was rich because of it, till they mined a bit too much of it and weakened the link in the chains that bound the end of everything.
Someone's already mentioned his (its?) involvement in the RttToEE...and then there's this...
I'm pretty sure in the D&D lexicon he is also the first (originally only?) deity that is referred to as both "mad" and dead/lost/imprisoned or whatever. The idea that there was something in the game multiverse that the
gods couldn't handle...and best they could do was, basically, pack him away somewhere was...a big concept with a big "Oh c---" factor.
Not [legally] having access to Cthulu and not yet codifying the concept of a "Far Realms" [the very idea of codifying such begins to give me a headache], Greyhawk had Tharizdun. So, yes, there is definitely a Cthuluesque flavor and draw. The other idea, that I think caught people off guard (and sparked the imagination) was the idea of a god of...insanity?! Not a demon. Not a devil. A GAWD!? A deity that was insane itself?!...but still knew what it was doing...? Not interested in conquering the world. Not interested in Evil eliminating Good. Interested in destroying EVERYthing, EVERYbody, ALL of the other gods, demons and devils...Tharizdun wants NOthing to exist! That was a big [and friggin' scary] idea.
Tharizdun is just a part of D&D's long, treasured [and begun decades before 3e was a glimmer in its daddy's eye] canonical history, as much as Hommlet, Bree Yark, Markessa, Eclavdra and Acererak.
So now, that card please. ;P