Long story short. My PCs are running around in Qbarra and eventually they are going to go beneath the temple of .... to stopp a cult from releasing Demogorgon and all that happy dappy do goodness.
Now my only problem is, beyond being the "creator" of the ettins, I don't really know what sort of traits to give him... I mean, Orcus has his undeath, Lolth has her spiders but Demogorgon... well he eludes me a bit so to speak.
So oh mighty voices of the interweb, do you have any sugestions as to what theme we could give Demogorgon?
Dualmindedness and save fury. Confusion, madness. Rage. Hate.
All that good stuff. 
Also this article might help, specifically the part about Monster Themes.
I actually wonder whether Demogorgon is better as a Rajah or Daelkyr. The standard route seems to be to make demon lords into rajahs, but with Demogorgon's dual identity, he could actually be the perfect creator of dolgrims and the other "two-smashed-into-one" monsters, whether ettins, hydras, etc.
As a rajah, his influence might be felt as burts of self-destructive fits of rage and manifestations of cruel alternate identities (perhaps linking him to werebeasts).
I agree. I was going to suggest making Demogorgon an aberrant entity that came over with the Dealkyr. He wouldn't be one, persey, but kinda just tagged along for the fun of it.
Either that or he's a creation of khyber like the rajahs, but remains an aberrant origin creature of savage cunning and fury mashed together. Like how the aboleths are khyber-spawn but also aberrants.
Demogorgon would probably best represent cunning, power and the driven desire to be the best, conflict at a hightened state. The duality of the Prince of Demons would reflect that even as the most powerful of Demons, Demogorgon is still in conflict and pushing himself to new scales of power (in this case, with himself). So I'd stick with the Demon origins rather than Daelkyr.
That being said, with all this whimpy peace, flower-picking and happiness post the Thronehold Accords, I'm sure Demogorgon is rather nauseated. Where is the violence, the bloodshed, the ever accelerating crash of technology to meet the new power level of each of the nations? The Prince of Demons must be itching to start the conflict again and watch as the petty mortals bring themselves to extinction and beyond...
Thanks guys, this gives me a few Ideas of what "themes" to use against my players.
As a demon, I think I would play him as an embodiment of conflict. In every legend about Demogorgon, there would be an element of this conflict beginning with extreme cunning, subtlety, and manipulation before ending in a bloody destructive rage where no one wins.
An interesting campaign idea just popped into my head. When ancient evils are involved, there are always extremely complex plots that the players have to unravel. Different groups want different things, and they cooperate, fight, and bump heads. But in this case, there is only one ancient power involved: Aameul and Hethradiah, each with different and opposing goals. No matter who wins, Demogorgon ends up free, unless the PCs realize it and stop every plot.
Actually, if the players don't know what they're up against yet, I wouldn't tell them. Let them think Aameul and Hethradiah are two entirely different foes.
...On the other hand, Demogorgon does make a great daelkyr. All those multi-headed monsters out there would finally have a good explanation.
Well given his beastly appearance, perhaps he could represent peoples inner battles with thier own inner savage and instincts, while trying to be above animals. Sort of like the idea of id, ego and super ego. Various concepts of self conflict.
I love that idea Gurv. Leave the players thinking "huzzah, we beat Am yet again", only to find out that it's all for nothing. Demogorgon still wins!