History of the Ashbringer

Corrupted Ashbringer
Binds when picked up
Unique
Two-Hand Sword
259 - 389 Damage Speed 3.60
(90.0 damage per second)
-25 Stamina
Requires Level 60
Equip: Inflicts the will of the Ashbringer upon the wielder.
Equip: Improves your chance to get a critical strike by 2%.
Equip: Improves your chance to hit by 1%.
Chance on hit: Steals 185-216 life from target enemy.
"Blade of the Scarlet High Lord"

This is the epitome of bad ass. The sword hits like a tank and steals life. But what interests me the most is the lore behind this awesome weapon.

Back story:
Ashbringer, the Blade of the Scarlet Highlord, is an object of great mystery and power.

One of the previous Highlords of the Scarlet Crusade, Highlord Mograine was known as the Ashbringer. Archmage Timolain crafted him a sword meant to be a bane against all the undead. It (and he) were called such because when he would take to the battlefield, his frenzied blows would fell the Scourge so fast that he would be surrounded in falling ash.

Several characters have mentioned the Ashbringer (or its maker Timolain) on occasion, but the only beings believed to know the current location of the Ashbringer are Nat Pagle, Master Fisherman, and Prince Tortheldrin, the leader of the Shen'dralar within Dire Maul. Getting the full story from them has proven difficult, but Tortheldrin's followers claim that he may be willing to tell what he knows if a player were to defeat the dragon Nefarian and share the tale with him. Some have brought Nefarian's head to Tortheldrin, though he said nothing that lead to the Ashbringer.

It now seems that Highlord Mograine was corrupted by Kel'Thuzad and serves him as a death knight in Naxxramas. He still wields the Ashbringer, though the blade has become corrupted as well. --WoW wiki

Where it drops:
The Corrupted Ashbringer drops from the four horsemen. The loot table of the four horsemen changes accourding to the order they are killed. Saving Mograine for last will give you a chance for the Corrupted Ashbinger to drop. If you're lucky enough to get this epic item you will be able to start a quest line to uncorrupt the Ashbringer, If you can find out how.

The Quest:
A korean guild has somehow found a way to start the quest chain. Here is a link to that information.

Apearently equiping the sword makes you friendly with the Scarlet Crusade and hated with the Argent Dawn. This allows you to walk into the Scarlet Monastary and chat it up with Scarlet Commander Mograine, whom just happens to be the son of Highlord Mograine. This triggers an event where a ghostly figure in full tier 3 Dreadnaught apears and starts a conversation with Commander Mograine. I found this translation online.

Mograine: son
Mograines Son: Father how?
Mograine: Do you think I forgot about your betrayal? I came here to pay you back. I am not bound by Kelthuzad anymore. Son! I come for justice. I am the Ashbringer and I shall have my vengeance.
Mograines Son: No! please, forgive me.
Mograine: You are forgiven my son.
After their conversation, Mograine kills his son in one shot. Then all the NPCs disappeared.

Realizing that theres one NPC trapped in the east corner of the room, he goes to the corner to talk to him. To his surprise, an undead (Fairbank) gets sanctified back into human and he expresses his gratitude for freeing him from the curse. Then he tells the player this long story about the history of Mograine and Ashbringer:

As you can see, thats a lot of material so I am just going to present a brief synopsis.

Mograine was a holy knight responsible for the founding of the Scarlet Monastery. During his time, the order embodied the true value of justice and its willingness to relinquish evil. But a tragedy has befallen where Mograines son betrayed his father by making a pact with Kelthuzad.
As planned, Mograine, Fairbank and his son were ambushed by thousands of undead soldiers. Mograines son fled but his father fought valiantly. While Fairbank being a puny ass, was slayed and buried deep beneath the bodies of the undead soldiers, he witnessed the scene where Mograines son held the Ashbringer and struck at his own father. In that instance, Mograine and Ashbringer became one, cursed with vengeful spirit.
Fairbank was able to escape and he alerted the son of Mograines betrayal to his fellow Scarlet Monastery members. Those who believed him established a new order called the Argent Dawn.

Now back to the sword:
Korean Player: Is it possible to cleanse this sword?
Fairbank: It is most likely that its too late to cleanse the sword that you have on your hand. The vengeance embodied within the sword is too deep! But dont loose hope. If theres an end, theres a chance for a new beginning. Find his son whos well known for his modesty and faith. It has been rumored that even without the Corrupted Ashbringer, its possible to construct a new Ashbringer.
Korean Player: What are you talking about? Hes already dead
Fairbank: You are wrong. You only killed one of them. The other still lives!

[High Inquisitor Fairbanks shakes his head]
No, orc! Only one of his son is dead. The other still lives.
[High Inquisitor Fairbanks points to the sky]
Outland...Go and seek him.
--www.ashbringer.com