My first OC was a demon contracted to his master and loosely inspired by Alucard from Hellsing.
The RP I used him for is long dead and even my best necromancy skills cannot crawl the web for the site I played him on.
So whatever I say I mention to you out of distant memories. It's been close to a decade now. For example I sure don't remember the character's name or any such precise details.

Well, on the character's background. Once upon the time a group secretly conducted a ritual to summon a powerful demon and supposedly attain immortality(?). They messed up and the demon went out of control, murdering near-everyone. Unfortunately the botched summoning also left him drained and out of desperation he made contract with the last survivor. This has been hundreds of years ago and since then the demon serves this family as their powerful servant. Mr. Demon obeys but of course he doesn't like his predicament and secretly plots for his freedom.

The basic setting was that after thousands of years the demons break the seal and begin invading the mortal realms again. To defeat them they gather seven or so heroes with legendary weapons. My demon was technically on their side, following his orders by his current master. He used to be a lieutenant of the fire demons and one of the most bloodthirsty and ferocious fighters known. Since having him roam around like that is hardly a smart idea he has 12 seals put on him.
Took quite a while to find it after several years but for his fully sealed form I used this pic:[hider=Sealed Form]
[img]http://orig03.deviantart.net/f1fb/f/2007/221/8/c/commission__speaker_of_chaos_by_wen_m.jpg[/img]
[/hider]

When fully sealed his personality is calm and sinister. He's still obviously bloodthirsty and uses something akin to a chain which he can control with his will. He also has a good degree of regen unless anti-demon/holy items are in use. As the seals come off he becomes stronger and more aggressive and can manipulate fire to increasing degree. After most seals came off he regains a considerable portion of his power along with his signature element the crimson flames (not sure on this part, maybe they didn't have any coloration). Its ability to grown in power the more area these fires burn make it a perfect weapon of massacre which may even surpass demon lords in this aspect. In short imagine a crazy demon made of nothing but living fire nuking everything. That's the true face of my character and that's the most likely situation if he's allowed to let loose.
Plus like I said he was plotting to free himself, with his comrades returning to the mortal realm he got a pretty good chance for that.
Until then mr. demon had no qualms about murdering anything else he was ordered to, be it even his fellow demons.

So yeah, that was him. Unfortunatelly the RP died down rather quick so I never had a chance to truly use him.