Not to be taken too seriously, just written for a site to get it as a link.
The Demonlord of Wrath, Maelik Rekjar, also known as "The War's Flame" or "The Fellblade" is rage incarnate. He feeds upon feelings of anger, hate and vengeance and seeks out those who exude such an aura of malice.
He walks the mortal world in hopes of seeing the world and all it has to offer rather than just observing it from his throne in the Circle of Wrath. He takes up residence in a darkened forest where he takes up the alias of one Iratus Ulciscor, a spindly armed lesser mage who lives in a humble hut. When he is not simply wandering around the country as the awkward twiggy meat sack disguise he shows his true terrifying form of a fourteen foot tall demonic monster. Closely resembling a black dragon he is immensely strong in both the physical and magical sense, as befits a creature of his breadth of experience. Still it takes a great deal of energy to fuel his presence on this plane and as such he must absorb a large quantity of negative energy. This can take the form of a dark thought or an ill intention, though more aggressive and violent forms suit his tastes much better.
He is adept in warfare and swordplay, pointedly with his dual greatswords, and he possesses the strength to crumple giants under his swings, though that isn't to say he is a slouch when it comes to magical might. He has mastery of fire, though the holy variety eludes his dominance. In addition he knows advanced shadow magic, rudimentary healing magic, dark magic and of course demon magic. But even with his incredible raw physical strength and eldritch talents his preferred method of combat is of the intellectual type. Having come to this realm not to conquer but to simply observe he prefers not to resort to violence unless pushed, seeking instead to settle disputes with games or challenges and if there is no other recourse than bloodshed he considers it a failure on his part. His motives are not entirely clear as he's really only here to enjoy the sights and sounds firsthand so he's more or less a wildcard, he may help or hinder any he comes across with an assisting hand or an insidious whisper to inspire the very negative energy he feeds upon.
Maelik wields two greatswords created from the deepest pits of the Abyss enchanted with the dark magics of black lightning. He wears a helmet made of tainted silver and has a set of magical armor that helps protect him from the attacks of mere mortals, though he relies more so on his demonic aura to dissuade attacks and protect him. He is a master of pyromancy and thanks to his demonic nature he is immune to fire both natural and magical (holy flame being the notable exception), has access to telepathy and can change his form at will, though the effort takes a good deal of concentration and drains his energy.
As would be expected of a creature of his stature he is immensely strong, able to snap bones and crush stones with his bare hands with little effort. In addition he is deceptively quick on his feet and on the come backs, his tongue just as sharp as his weapons. With his natural demon constitution he is hardy and difficult to seriously hurt as well as boasting an impressive ability to regenerate from even the most grievous wounds. Even in death he is not down for good, as his essence merely returns to his hellish homeland until his body can reconstitute itself, though the trip back into the mortal realms is difficult and requires a helping hand from either a gathering of willing spell casters or one of immense magic talent.
The Demonlord, while imposing, is not invincible. In fact he is far from it as he has a few heavy weaknesses. One of which is his vulnerability to intense cold. If a cold/ice aligned spell can pierce his fiery aura he gets slower, his demonic protection weakens and his attitude takes a sudden turn for the worse. He is also more weak to divine or holy magic than the average creature but thanks to his higher status and power he isn't as screwed over by it than his brethren. The final and definitely most bizarre weakness is his overly sensitive tongue. Its primary use is that as his tracking device, much like a snake he flicks out his tongue to smell the air around him in order to sniff out the guilty (and his meals.) But thanks to its excessive sensory functions anything that can punish his sense of taste can actually mess with him, in some cases it can even momentarily stun him.