DS Lore

Dark Souls is a world of cycles. On the macro scale between Ages of Fire and Dark, and on the micro scale with the curse of undeath causing humans (including the player) to return to life, losing a bit of their Self each time as they 'go hollow'.

The Age of Ancients was the original state of the Dark Souls world, with unchanging trees, dragons, and fog summing up existence. The sparking of the First Flame underground put time itself into motion. From the flame, the Furtive Pygmy claims the Dark Soul and splits it into innumerable shards (humanity), bestowing them on its descendants (hollows, which became human with this gift). It then disappears from recorded history, setting into motion a long Thinker game on the span of Ages.

Separately, three beings claimed the other Lord Souls, Gwyn - Light, Witch of Izalith - Life, and Nito - Death, turning themselves into living gods, much stronger than individual humans.

The three Lords fought the dragons to claim the surface, to no success. Seath was salty he couldn't play with all the other dragons, so he sold out the secret of their immortality - lightning strips their otherwise impervious scales. So Gwyn blows away their scales, the Witch of Izalith burns their homes to deny escape, and Nito kills them with plagues, leaving Seath as the last true dragon. Thus starts the Age of Fire.

Gwyn builds Anor Londo as his capital atop a mountain to be near the sun. Nito is content to play with the dead underground, while the Witch of Izalith studies original pyromancy (much stronger than the faded versions the Chosen Undead - the player - gets access to).

For Seath's service, Gwyn made him a duke and gave him a lab to conduct his experiments seeking to understand immortality (by consuming commoners, angering them).

Havel the Rock, a loyal knight under Gwyn's reign, takes umbrage against Seath's experiments. He gathers a group to kill Seath, so Gwyn locks him away to suffer a Hollow fate. The experiments drive Seath mad, though he plundered the Primordial Crystal during the war which grants him immortality while it endures.

This Abyss is a physical region powered by the net darkness found within humanity, and it threatens to snuff out the First Flame if left unchecked. There's also Kaathe, the primordial serpent who desires the Age of Fire to end. He convinces Oolacile, a town atop the Abyss, to dig up the grave of Manus, the first human. Manus goes insane when resurrected, his Humanity spirals out of control (consuming and corrupting Oolacile's residents), which accelerates the growth of the Abyss.

Gwyn sends his trusted knight Artorias and his wolf pup Sif to Oolacile to contain the Abyss. Artorias confronts Manus, loses, and is corrupted. Manus looks across time and space for his treasured pendant, finds it in the future on the Chosen Undead, and pulls both back in time to him. The Chosen Undead defeats Manus, saving the world from the Abyss, and protecting Sif.

Much later, the First Flame begins to fade. The Lords panic over the source of their power (and continued existence) failing, as only the Dark Soul can sustain its extinguishment.

The Witch of Izalith tries to create a Second Flame as the pinnacle of her long studies. She fails catastrophically, and instead births Chaos into the world. It corrupts her into the Bed of Chaos, and all of her children become demons - save Quelana, who escapes this fate by being far from Izalith.

As a last-ditch effort, Gwyn sacrifices himself to the Flame, using his soul to rekindle the fire. This works, renewing the life of the Flame as long as he sits within it. He becomes the first Lord of Cinder, a creature who has enough power to sacrifice itself to rekindle the Flame.

Becoming a Lord of Cinder is only a temporary solution, delaying an inevitable Age of Dark. Additionally, by rekindling the Flame, he has cursed humanity with immortality. Undead humans always come back, but the more they die, the more they become Hollow as their Humanity fades.

The Chosen Undead awakens, and they tacitly accept the prophecy of rekindling the Flame. They strive to gather enough power to sacrifice themselves and become a Lord of Cinder, at least according to prophecy.

To do so, they have to reach the Kiln of the First Flame. To open that pathway, the Chosen Undead needs to reinforce their soul to equal a Lord's, by collecting the Lordvessel and the fragments of Gwyn's soul he imbued his knights with before his sacrifice. They sacrifice these fragments to the Lordvessel, which provides access to the Kiln.

Within this Kiln, they find the cindered husk of Gwyn. It attacks as a final check against an insufficient soul linking the fire. You can rekindle the Flame, as the prophecy intended, or you can let it die. If you choose the latter, the Chosen Undead becomes a Dark Lord, and the primordial serpents unite under Kaathe's faction to worship you for ushering in the Age of Dark.