In the beginning, there was nothing. The world was empty and formless.
For eons, man as we know him did not exist, and the world was ruled by the Everlasting Dragons. The scales on their hides provided them with immortality, and save for the giant ashen Arch Trees that served as their homes, the land was nothing but a gray and desolate wasteland.
... then, seemingly out of nowhere, the First Flame burst forth.
This fire created light and dark — and out of this darkness crept humanity. Thanks to the power of the First Flame, mankind was granted souls and began to evolve. Four extremely powerful souls, known as the Lord Souls, came forth and granted their bearers extreme, godlike power: Gwyn became the Lord of Sunlight, Nito was the First of the Dead, the Witches of Chaos were formed ... and finally, the Furtive Pygmy took its Dark Soul and withdrew into the Abyss.
Years passed, and the Undead Curse swept over the land. In a desperate attempt to find a cure, an Undead known as the "Bearer of the Curse" risked the trip to Drangleic. Upon arriving, the Bearer is tasked with gathering four Great Souls — only they are powerful enough to break the seal surrounding Vendrick's castle.
The Old Iron King, the Lost Sinner, the Rotten and the Duke's Dear Freya all fell to the Bearer's blade, and the path to Drangleic Castle opened. As Nashandra watched over them, the Bearer discovered what was left of King Vendrick — a hulking, mindless Hollow. However, while Vendrick may not have offered any answers, his ring did — and it pointed the Bearer toward an ancient castle known as the Dragon Aerie.
The ruler of the Aerie, the Ancient Dragon, provided the Bearer with a unique tool: the Ashen Mist Heart. With it, the Bearer traveled into the memories of those who had fallen long ago — and in the memory of the final battle between the Giants and mankind, the Bearer found the key to the Throne of Want. However, after fighting their way back through Castle Drangleic, the Bearer found someone waiting for them.
The Queen of Drangleic had always assumed that, as soon as she had found a way past Vendrick's defenses, the Throne of Want would be hers.
She was wrong.
The battle between Nashandra and the Bearer of the Curse was vicious, but ultimately, it was the Undead human that stood victorious. Like hundreds of years prior, they were given a choice: either re-link the First Flame and ensure that the Age of Fire would continue, or step away from the throne in search of a more permanent solution.
In the end, no one knows exactly what happened after the Bearer defeated Nashandra. Given just how devastated the world appears to be in Dark Souls III, it's entirely possible that the Bearer chose to follow in Vendrick's footsteps ... but until the game's sequel launches, there's no way of knowing for sure.
Thankfully, the wait won't last much longer: Dark Souls III is scheduled to launch on March 26.