Knight Artorias

"Thou shalt see further on, an Abyss was begat of the ancient beast, and threatens to swallow the whole of Oolacile. Knight Artorias came to stop this, but such a hero has nary a murmur of Dark. Without doubt he will be swallowed by the Abyss, overcome by its utter blackness... Indeed, the Abyss may be unstoppable..."

- Elizabeth on the Abyss and Artorias.

Knight Artorias is the titular fallen hero of the Artorias of the Abyss DLC from the 2011 action role playing game Dark Souls. Originally a knight who attempted to free Oolacile from the possession of Manus, he was corrupted by the Abyss he was destined to destroy.

Backstory
Artorias was once one of the Four Knights of Gwyn alongside Dragonslayer Ornstein, Hawkeye Gough, and Lord Blade's Ciaran. Known for his unbreakable will of steel and admiration for greatswords, Artorias was trained to combat the Abyss that leaked from underneath the kingdom of Lordran. Accompanied with his wolf companion Sif, Artorias fought the Darkwraiths who had since fallen from grace. For his actions he was gifted a Silver Pendant that deflects the spells of the Abyss. Supposedly, within the ruins of New Londo, Artorias made a covenant with beasts that have not yet been corrupted and was granted a special ring that allowed him to enter the Abyss itself without being consumed, thus giving him the alias "Artorias the Abysswalker".

Artorias would then hear of Oolacile, a place corrupted by the direct source of the Abyss itself, an sorcerer by the name of Manus. While Ornstein stayed behind to guard Anor Londo, Artorias, Ciaran, and Gough ventured to Oolacile. While the other knights fought against the infected citizens of Oolacile and Gough attempted to settle his score with Black Dragon Kalameet, Artorias and Sif entered the Abyss to engage Manus and rescue Princess Dusk.

However, when Artorias actually entered the Abyss, he was completely overwhelmed by the darkness. Deeply marked by the Abyss with his arm broken, Artorias had no choice but to abandon his shield to protect Sif with a magic barrier and was corrupted by its influences. He later emerged from the Abyss, not as his regular self, but rather an alteration deprived of spreading the Abyss.

Battling the Chosen Undead
When the Chosen Undead was brought to the time of Oolacile from Manus, they encounter Artorias within the coliseum of Oolacile Township at the end of the Royal Wood. After killing a Bloathead citizen within the arena, the fallen Abysswalker battles the Chosen Undead, only for the Chosen Undead to defeat him. Ciarian would tribute where Artorias would fall and grants her weapons to the Chosen Undead should they give her the Soul of Artoias, and Hawkeye Gough thanks the player for putting Artorias out of his suffering.

Legacy
Despite Artorias being corrupted from the Abyss, the belief that he rather died fighting the Abyss stood instead. As such he was seen as a hero through all of Lordran. His corpse was buried in the Darkroot Garden, guarded by the Forest Hunter covenant and by Sif, watching over his master's grave. Defeating Sif makes him drop the Covenant of Artorias ring that is mandatory to enter the Abyss to fight the Four Kings.

His legacy also carried over to the kingdom of Lothric, where the Abyss Watchers partook the wolf blood and bound their souls to the "wolf blood master". The legion took after their inspiration in fighting off the Abyss that threatens their home. But in a sad twist of irony, they too became corrupted of the Abyss much like their posthumous idol.

Appearance
Artorias is a tall figure wearing silver armor decorated with blue cloth. His face is hidden behind a hood. Since becoming corrupted by the Abyss, Artorias has a shadowy aura emitting from his body. He leaves puddles of a black liquid where he stands.

Personality
Once known as one of the most loyal, caring, and trustworthy knights of Gwyn, Artorias has since became insane from the power of the Abyss. He expresses the lost of his sanity before the boss fight by mercilessly killing a Bloated citizen, throws it at the Chosen Undead, and howls like a madman during the fight before some of his attacks.

Trivia

 * Artorias has unused dialogue found in the game's files.
 * It is speculated that Ciarian and Artorias has some sort of romantic relationship. From Gough, Ciarian's affections were not returned.
 * Artorias is the only boss not to drop Humanity.
 * Artorias' deep breaths can be heard outside the fog wall.