Knight Artorias, also known as the 'Abysswalker', was one of the four knights of Gwyn.

When Oolacile fell to the dark, he was awarded the Silver Pendant for facing the Abyss, an ancient treasure of Anor Londo that "deflects the Dark of the Abyss, especially in its magic forms". He travelled to Oolacile but was defeated by Manus. Artorias sacrificed himself to protect his wolf companion, Sif, using his great shield to raise a barrier around the pup. He fled from Manus, but his exposure to the abyss overcame him and he fell to its corruption. By the time the the Chosen Undead arrives, it is too late; Artorias is by then completely overtaken by the corruption of the Abyss and attacks the player.

His grave, marked with his greatsword, is placed at the Oolacile Sanctuary area (later known as the Darkroot Garden) and is guarded by Sif, Alvina's clan of Forest Hunters, and possibly also Lord's Blade Ciaran.

The "beasts of the abyss" are generally accepted to be the primordial serpents.

It is clear that Artorias gained the ability to traverse the abyss without being completely consumed. More specifically, it was either Frampt or Kaathe that Artorias made the pact with.

Kaathe was thought to be responsible for convincing the people of Oolacile to dig up Manus, as he generally wants to see Humanity propagate by any means.
Artorias may have been deceived into being corrupted. Or, it may have been Frampt to mess up Kaathe's plans, which is more in line with the legend of Artorias going to Oolacile to fight Manus.

Based in Farron Keep, the Abyss Watchers are a group of Undead warriors who acted in the dark, seeking out any sign of the Abyss, fighting a constant war with its abominations. They "vowed to partake of wolf blood". Slightly ironic, or possibly intentional, as Artorias the Abysswalker's companion was Sif, the Great Grey Wolf.

Being of Farron, they were lonesome warriors proficient with the sword, and relied only on more pragmatic spells. It is unknown whether one or all of the Abyss Watchers linked the fire. Perhaps they worked together to push back the darkness. But, they were betrayed by the Fire. The wolf blood that bound them to one another dried up, and Farron "was consumed by a festering wood".

The very power the Abyss Watchers drew from to combat the Abyss evaporated in the fire. Their home grew acrid, and the allies they left behind were warped into inhuman creatures.

Worse yet, the Abyss was left unchecked, and now Darkwraiths roam freely in Farron, an affront to everything the Abyss Watchers stood for.

Now the watchers sit on the doorstep of the darkness they once sought to extinguish in the Catacombs of Carthus.