Xandu

The world was young once. Dragons roamed the skies nesting in the highest peaks. Monsters roamed the lands, taking what they could, eating what (or who) they wanted, and making the land their own. the Denizen of the lands did the best as they were able. The Elves stayed in their forest fortresses. The forests themselves were dangerous enough. Dwarves hid among the mountains, away from the prying eyes on the surface. Like the Elves, life in their domain wasn't easy. The minor races lived as best they could in their homes, dealing with what life tossed at them. And then there were the Humans. Whereas the rest of the races were either content as they were or unable to change the status quo, humans were decidedly not that the case.
It started as a trickle. A few adventurous souls to explore the unexplored. Finding the land difficult, but prosperous, various groups continued to come forming settlements along the Southern edges. And they did not take lightly to encroachment. These were a hardy group. It didn't take too long before monsters, except for the very strong, found easy pickings elsewhere. Outposts grew to villages. Villages grew to cities. And eventually cities and the different nationalities began to contest resources. Because humans are humans, the best way to settle conflicts is through violence. In the end, over a long period of time, the Southern portion of the continent became what is now the Southlands.
It was during this time upon one of the earliest ships that a talented mage named Xandu set his foot upon the sands of Alkeria. He was looking for more than adventure. He was looking for power. He was a tall for a mage with the bright red hair typical of most human mages. Most found him friendly enough, but intimidating. As they should be. Xandu was not one to be taken lightly as others had found before.
Xandu joined several adventuring parties to scout the Southern portions of Alkeria for various groups. He found the adventurers to be petty and ineffective. After several missions, he decided to adventure on his own. Travelling through the untamed wilds today is a dangerous task. In the days of old, it was just about suicidal. Xandu didn't let that bother him. Rumor has it, he encountered a few monstrous rock lizards very early that, after some magical retraining, served as his muscle for months. He never seemed to have an issue.
And Xandu explored. Up through the Southern Alkeria to the Bloodwood Forest where me the Elves. He travelled northwest to the mountains where he met the Dwarves and where he caught his first scent of power. He travelled east across the northern wastes where he caught his first scent of power. At the base of dwarven mountain at a signpost indicating the dwarven domain, there was an exposed node of magic. He could feel the trickle of it as he passed through. That little trickle energized him to something beyond anything he'd felt before. And he wanted more.
Following the direction of magic, Xandu scoured the northern wastes looking for the source. Deep in the northern mountains, he found it. He only needed to kill the dragon hoarding it to claim it. The battle was epic but Xandu survived, burnt, bloodied and scarred. But the magic was his.
And thus began the time of Xandu. Alkeria was a magical focus. The beasts were of a more magical nature, the inhabitants had an easier time harvesting magic, and the environment was generally a bit more unnatural that other places in the world. Xandu began siphoning that magic directly from the source, and his power expanded exponentially. He became the single most powerful creature walking the continent.
The natural beasts bowed to his power, and the inhabitants whether they liked to or not, were forced to worship him as a god. Even most of the dragons died as they attempted to unseat Xandu as the force of power he was. Nothing changed and Xandu became more and more powerful. Xandu's aspirations became bigger. He was too big for this world, and began determining how actually CHALLENGE the gods. By denying followers of the other gods, he had a head start, and began formally and systematically hunting and destroying worshippers and places of worship of the others.
Upon Xandu's discovery, the gods simply watched. It was nothing of real concern. Most who find that kind of power were generally able to destroy themselves with it. Xandu was different. He had managed to figure out a way to harness it. By the time the gods figured this out, it was nearly too late. The wheels were already set in motion and it'd take too much time to reverse or change course. So the gods had to do things differently. They chose their champions.
In one of the very few times in recorded history the gods of old came together for a common cause. They each infused a portion of their life force into a champion. The gods of the demi-humans were asked as well, but were refused; either by being not powerful enough, by it causing a loss of safety for their people, or that Xandu was providing them a benefit. Needless to say, that didn't go over well. The Champions; one each for Life, Death, and Balance spent their lifetime evading Xandu while searching for the keys to undo the magic lines that fed Xandu's power. With the help of some spies, they discovered his weakness, and were able to confront him.  The end result being a cataclysmic blast that is now known as (the black).  
Nobody quite knows what happened during that time.  Xandu was never seen again.  The power base that Xandu had created quickly fell into chaos as the various monsters and generals took advantage of the power vacuum.  Without Xandu to maintain control, the hordes quickly returned to more traditional hierarchies which generally did NOT work well together.
For himans, Xandu is only remembered in stories.  Older dwarves and elves will remember the times of Xandu, but for most humans, he's a myth. His sealing was 250 years ago.
Two years ago, there was rumor of a town on the east side of the continent along the Continental road (TBD) that was destroyed. Since then, several border towns have been destroyed in a path of destruction heading north. Since then, reports have filtered in of hideous monstrosities that have been seen in the north, and while most don't believe it, the rumor of Xandu's return is whispered in back corners of taverns and in secret societies.
His actual status is unknown to this day.