Knight Artorias

Knight Artorias also known as Artorias the Abysswalker is a boss in Dark Souls. He is exclusive to the Artorias of the Abyss DLC.

Location
In the colosseum area of Oolacile Township, at the end of the Royal Wood.

Description
By the time the chosen undead encounters him, he is shown to have already been corrupted by the Abyss; the reason for his armor's putrefied appearance and the aura of darkness that oozes creep. His crippled arm is likely the result of Artorias halting the spread from devouring his wolf companion by means of a [now missing] shield. He posseses a greatsword that has also been consumed, yet is still far from ineffective. Having lost his sanity, the knight moves about in an untamed manner as he howls beneath the blue shroud of his helm.

Lore
Sir Artorias the Abysswalker was one of the Four Knights of Lord Gwyn. He only makes an appearance in the past as he is deceased by the time the Chosen Undead escapes the Undead Asylum.

Knight Artorias wore distinctive armor, as well as the Wolf Ring and brandished his Greatsword and Greatshield. He is also known to have been a friend to Alvina of the Forest Hunter covenant and Sif, the Great Grey Wolf, who guards his grave and keeps the Covenant of Artorias ring in his possession.

Artorias hunted the Darkwraiths and was able to traverse the Abyss with the power of his ring, which he gained after making a covenant with the beasts there, preventing him from being swallowed by the void and cursing his sword. In recognition of his actions, he was awarded one of Anor Londo's treasures, a Silver Pendant that allowed him to repel Dark sorceries.

When Oolacile became threatened by the Abyss created by Manus, Artorias and his wolf companion, Sif, arrived there to save Oolacile and rescue the abducted Princess Dusk. However, the two were overrun and Artorias sacrificed himself to protect Sif using his Cleansing Greatshield, erecting a barrier around the young wolf. Swallowed by the Dark, he became corrupted along with his sword. He was then finished off by the Chosen Undead after the encounter in the colosseum of Oolacile.

Overwhelming Leap
Crouches, then leaps high into the air attempting to land on the player, causing damage in an area of effect around him. Rolling or moving towards him, instead of away, can increase one's chance of successfully dodging him before he lands.

Somersault Attack
Somersaults into the air and slams his sword down vertically. He can repeat this up to three times. Roll to the side to avoid it. Artorias can stunlock the player in this combo.

Heavy Slam
Slams his sword overhead towards the ground, high staggering power, but leaves his guard open for a short time after it lands.

Heavy Spin
Dashes and spins with his sword. He presents an opportunity to be attacked after it lands.

Heavy Thrust
Pauses before performing a heavy thrust towards the player. If it connects, it has the potential to hit twice, dealing heavy damage.

Spin Attack
Quickly spins, completing two full revolutions.

Abyss Sludge
Throws black sludge in a wide arc in front of him.

Wrath of the Abyss
Activates in intervals after approximately 20% of his total health is reduced. After backing off, he slowly builds up magical energy, presenting ample time for retaliation or to apply augmentations to one's weapon or self. He releases it in an explosion that does Magic Damage in a mid-ranged area of effect which completely surrounds him. He becomes supercharged for a time afterwards, hitting harder and causing more damage. However, he is vulnerable while charging and can be stunned with consecutive hits from a strong enough weapon.

In addition to the health thresholds, this attack has a time interval between uses, in that if Artorias is left undamaged for a period of time, he will re-activate Wrath of the Abyss.

Trivia

 * Artorias, like many characters, had unused content that was hidden between the game files. Here is the dialogue that was kept out of the final version. Artorias was supposed to have the same voice actor of Griggs of Vinheim.
 * It's implied in his cut dialogue that Artorias was not human like the rest of the four knights.
 * It is speculated that Artorias had a romantic relationship with Lord's Blade Ciaran before being corrupted by the Abyss.
 * Artorias has severely injured his left arm, to the point of being limp, sometime before the player fights him. It is also believed that Artorias left his Greatshield with Sif in the Abyss after he suffered the injury..
 * Artorias' design may have been based off of the character Guts (also known as Gatts or Gattsu), the main protagonist of the manga series Berserk. Many similarities can be found between the two. Both Artorias and Guts use a greatsword and have a handicapped arm (Guts has a prosthetic left arm), and Artorias's Sommersault Attack is very similar, if not the same, to Guts's Spinning Jump Attack when he wore the Berserker Armor. In addition to this, Artorias has a wolf companion, Sif, whilst Guts has an inner canine-like personality, which is named Hellhound.