One of Gwyn’s Four Knights, Sir Artorias is a holy warrior with an unbendable will of steel and unmatched skill with a greatsword. His personal symbol is a wolf, as depicted in his ring, and he later gains a wolf companion named Sif. He makes his formal appearance in the Additional Content.
Artorias was present during the fall of New Londo. The home of the Darkwraiths, the Abyss, can only be traversed by the creatures of the Dark. To be able to destroy it from the inside, Artorias made a covenant with the creatures of the Abyss, symbolized by a ring. But in doing so, his greatsword became cursed. In recognition of his actions in the New Londo crisis, he gains the moniker “The Abysswalker” and awarded one of Anor Londo’s treasures, a blessed pendant that allowed him to repel the Dark of the Abyss.
When Oolacile woke Manus, Manus’ influence corrupted the citizens of Oolacile against their will and made them the forces of the Abyss. Artorias, accompanied by Sif, arrived there to save Oolacile as well as Princess Dusk, who was captured from the present day. However, the two were overrun by the creatures of the Abyss. Artorias sacrificed himself to protect Sif using his greatshield to raise a barrier around the wolf pup. Defeated by the Abyss, the knight became corrupted against his will.
His already-cursed sword became corrupted by the Abyss as well. But even with one arm broken, Artorias is still a formidable swordsman (some of his technique is later used by Sif in Sif’s boss fight), as you will find later when you fight him before entering Oolacile Township. 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.