Demon Lord Orcus himself (in 1st edition stats). Then this follow up post covers a new summonable demon servant of Orcus, The Enfrahl. Grodog writes:
"The Enfrahl are surreal horrors created through the whimsy and caprice of the Lord of the Undead---a cross between ossified guardians, bone sculptures as performance art, and sentient, demonic knick-knacks, the enfrahl represent all that is twisted and grotesque in the imaginings of Orcus and his ilk. That they are intelligent and aware is all the more damning….” --- Iscladoc the Dark, from his _Commentaries on The Demonomicon_."
Anyone looking to explore more about the Prince of the Undead and his minions will find grodog's insights useful for their campaign. Enjoy!