Disclaimer: First off, this NPC could operate under a number of different 'influences' even though I stuck him under major. Second, I apologize about the length, to me it seems long, and in my mind I could have made it longer. But in the interest of keeping my audience, I abbreviated some things that definitely could have been expanded upon. Thirdly, I'm sure that the idea of an uber being, even power stripped, will not be everyone's particular brand of vodka. If it isn't, don't feel you need to waste your time here.
Khelekgundhal is a demon lord. He is a shapeshifter and has no true form, however he prefers three different forms.
First form is a demonic looking humanoid in diabolical looking black and silver field plate. He has three horns sprouting from his bat-like head and bat wings sprouting from his back. This is kind of his default form, which he mostly identifies himself and which he usually takes in dealing with beings who could be considered his peers. His second form is that of a giant star-nosed mole covered with metallic scales. The “star” nose is used as a mass of tentacles (with great versatility due to his shapechanging nature). This form is his primary form for doing battle with armies/crowds of mortals. He has enjoyed many a surprise attack by burrowing into a strategic location. His final form has a few variations depending on circumstance and is for pleasure seeking moments. I'll leave it to your imagination if you don't mind.
Over his considerable lifetime he has mastered many hidden magiks and mind powers in addition to being an expert in multiple forms of combat. At the height of his power he was formidable foe for most gods.
The Worm -
Khelekgundhal has something inside of him which he calls the Worm. It has never been seen. However, it feels to him like a worm with razor sharp teeth forever chewing it's way through him (at times with incredible speed). Without a doubt this causes him an extraordinary amount of pain. His natural rate of healing tends to keep him alive despite this thing which seems determined to eat him from the inside out. Strangely the worm seems to have some kind of telepathic link with Khelekgundhal. It stops eating him for several hours at a time after Khelekgundhal his made a kill (sometimes days after a massacre). This has prompted Khelekgundhal to go into beserk rages in the past, lashing out at anything and everything just to get some relief from the pain. He has gone through great lengths to remove the thing from his body, utilizing his own shapechanging ability, magic, psionics, self mutilation, bargaining with other beings of extreme power but no one can seem to detect the Worm let alone get rid of it. Once every 97 years the worm falls asleep as it were and “disappears” for approximately 13 months giving Khelekgundhal some rest. After the 13 months, Khelekgundhal always faces the return of his tormentor.
History – short version
Khelekgundhal was born many tens of thousands of years ago, he honestly can't remember, it feels like an eternity. With his own birth came the birth of the Worm. His parents immediately noted his troubles and tried to direct his rage against their enemies. The details of that conflict are forever lost although it can be noted that both the enemy of the hour and his parents did not survive, all slain at his hands.
A Time of Strife
Afterward he became a slave to his passions and embraced the bloodlust to seek the relief it provided. During this time he used dimensional travelling to pick different worlds to attack and get his fill. The enemies he created are countless. After a time, and multiple near death experiences, Khelekgundhal realized he could not go on this way and a hope that this could end and he could get control of himself began. He searched many years for a cure before falling back into his carnage “rut”. And again for the cure. Back and forth many times he went. In his bargainings, many bad deals were made and from some of the “unbreakable” contracts that were formed, he was forced into slavery to evil gods for a few centuries. After that, there was a time when he embraced pure evil. He moved completely into a fantasy dimension which was controlled by a small patheon of five dieties. Using trickery he learned from his unsavoury acquaintances, he managed to capture and imprison all five dieties. He spawned several new races of demons and worked at corrupting the mortals hoping to use their souls as currency to buy his cure. The mortals of the dimension he chose were sadly (for him) quite resistant to darkness and caused no end of trouble for him, constantly slaying his demon servants, invading his fortress, and otherwise resisting his efforts. During one such terrible time, Khelekgundhal lost his temper and began to destroy a city. With the worm pacified momentarily, Khelekgundhal felt a new pain as he looked down upon the body of a young child he had just slain. He felt like a slave again and his anger took him away from the battlefield that hour.
A Time of Learning
Khelekgundhal began a quest for the most powerful magics known. He was determined that if no one could help him, he would have to develop a cure himself. He explored numerous dimenions in his pursuit of magic. For a century or so he was deeply interested in potions that have the strength to permaneantly alter the imbiber. He also expanded his mind and unleashed many dormant psionic abilities. One day, to his utter dismay, he learned he needed the blood of his parents to cure himself. A decade of further searches left him hopeless. He was certain he could not be cured without the blood which had long since been spilt.
A Time of Teetering
At this time, Khelekgundhal was experimenting with everything. He married several times during his breaks. Sadly the relationships did not last much past the 13 months. He went on several good crusades just for the experience, he suffered torturous surgeries in an attempt to catch the Worm, he granted a mortal “3 wishes”, he tried to make a new race of dragons, he got some revenge on one of his former “masters”, he enchanted himself with a strong empathy spell and instilled in him every emotion felt by humans for up to one month an emotion, he tried to create a moon, he joined in a demon sponsored attack on a devil's operation, and he became a vicious rooster (attacking a farming community and creating a new poultry phobia), just to name a few of his endeavours. (Basically, he's tried everything)
A demon servant of a friendly “acquaintance” (Khelekgundhal has no friends, only underlings, acquaintances, and enemies) showed up at Khelekgundhal's fortress. He promised a cure based on an ancient ritual magic stolen from an Old One's mind as it slumbered. The ritual involved the building of a throne made of angel skulls, a rare dragon skin, huge diamonds, his own blood, unicorn horns, and many other rare and 'near impossible to locate' ingredients. The servant insisted the cure was guaranteed and when cured Khelekgundhal would turn over his whole operation (including the 5 imprisoned dieties, underlings, and so on) as payment. Khelekgundhal was skeptical but agreed as this was just an agreement with no blood signatures and contracts.
With the throne all but complete, Khelekgundhal sensed the power of the artifact he was building and gave into the excitement of the moment. A greater demon underling of his then warned him an intruder was spotted in the fortress, but Khelekgundhal ignored the warning as intruders were not that rare. With the throne complete he sat in it and activated it using the power words.
Suddenly he found himself in a far off dimension, lying on a straw matress in a building of some kind. Hovering over him was a hooded figure. Realizing he'd been betrayed, he invoking his Storm of Metal Splinters spell and attempted to destroy his betrayer. The spell, which usually kills anything you're looking at, fizzled into nothingness. Reaching out with his mind he attempted to turn his opponents mind into a little puddle of grey mush. Again no effect. He tried to rise but the figure easily kicked him down. It was then that he realized he was in a human body.
The figure then gave him a monologue about how sweet the revenge was, how pathetic Khelekgundhal is, and how he could kill him right now so easily but how he wanted to watch Khelekgundhal suffer. Promising to return later to finish the job, the specter vanished.
Khelekgundhal lied on the bed for a few moments more narrowing the list of his enemies who could pull this off and reached a number of almost 50. Suddenly the revelation hit him, he didn't have the Worm with him anymore. With that an innkeeper opened the door and promptly evicted the impoverished stranger who apparently snuck a night's sleep at his inn.
Khelekgundhal does not hate being human. It does make him feel vulnerable but the break from his pain makes him feel in no big hurry to get his power/body back.
Yes in this human form, Khelekgundhal is pretty powerless, all the spells he knows require way to much energy, his psionics are temporarily blocked, his fighting ability is almost non existence (although he is bound to know a many tips to help any fighter improve his ability).
Khelekgundhal may or may not be evil (or an antagonist) even though he is a demon lord and has been evil in the past. He is most interested in self preservation and may ally himself with a party of adventurers and even identify items or translate different languages or other scholarly type help if the adventurers will take him along. He is unlikely to betray them unless the situation grows desperate. His conversion to "good" is entirely up to the needs of the campaign and could sway at any time.
The Specter did not kill Khelekgundhal because if it does Khelekgundhal will return promptly to his fortress, as his old self, and be seated on the throne again. The fully empowered Khelekgundal would then have full power to scry the truth and take revenge.
Khelekgundhal would most likely avoid the clergy and/or paladins as they may be able to discover his true nature and want to act on it promptly. Khelekgundhal will not enter a temple of any kind on purpose and has a huge chance of being discovered if taken there.
Khelekgundhal is unlikely to fight in this form as he is aware of his new limitations and how easy it is to die. He will not knowingly break the laws of the area and attract negative attention.
If Khelekgundhal joins the party, his personality will bounce between being overly commanding (with that demand for respect in his voice and countenance) and being sullen and self contained.
Possible Plot Hooks -
Khelekgundhal is the oracle the party has been visiting. Perhaps some of the information given the party is skewed in his interest of self preservation.
The mystery being plaguing Khelekgundhal is the same being as the PC's arch-nemesis (or they are closely related i.e. boss/henchman, brothers, god/champion/follower etc.)
Khelekgundhal is a peddlar the PCs come across selling potions (healing) and whatnot (he has the know how if the herbs & ingredients are available). Perhaps his wares are better than normal or have a side effect, provoking a response from the PCs
Khelekgundhal could be a prisoner due to the problem with the inn keeper or another sticky trap the hooded figure set up for him and meet the PC's in prison (if they are prisoners also). Perhaps with Khelekgundhal's knowledge and the PC's equipment/muscle/natural abilities an escape could be pulled off.
Khelekgundhal might act as a “deus ex machina” with the right information or potion at the right time to really save the PC's collective butts then to have his cover blown and have a lynch mob form from locals putting the PC's in a dilemma.
Khelekgundhal, having been abused by the dregs of society since becoming human, finds a ritual way of pulling off one of his severe god spells to crush a local community. The PCs are their only hope.
Khelekgundhal employs the PCs to take him to a location of an old (not functioning) dimensional gateway. Although the PCs think they've been hired for another purpose. If he reaches the gateway, he has the know how it light that baby up.
If you think the players would go for it, get them to help Khelekgundhal get his powers restored. Could be a big deal with a huge/interesting reward at the end.
If you think a player could handle it. Get someone to play Khelekgundhal in your campaign. Give him a handful of useful abilities that are easier to manage and see how it unfolds. Personally, I tried this once and found it difficult having a know-it-all in the party. It still had it's moments.