The Ashbringer  
    The Ashbringer sword was supposedly created by the Archmage Timolain for the Scarlet Crusade, along with other weapons. The sword is also connected to the infamous fisherman Nat Pagle, and the prince of the Shen'Dralar, Prince Tortheldrin.
 
    The name "Ashbringer" refers to both the sword of legend, and to the original wielder of the sword, Highlord Mograine. A great champion of the Scarlet Crusade, he gained his nickname from his soldiers, who would watch him wade into battle, cutting a blazing swath of holy light through the legions of undead, leaving nothing but ash in his wake. The sword of the Ashbringer was thought lost, but rumors of it's location have persisted through the years. It is spoken of from the Plaguelands to the deepest reaches of Kalimdor. And now, the truth of it's location draws near....

Rumors and speculation about, but now the story is slowly unfolding. Read on for details...
 
The corrupted version of the sword drops from the Four Horsemen inside the Naxxramus Necropolis. The order is unimportant, unlike some of the other multi-boss raid encounters. Once you equip the sword, you can enter the Scarlet Monestary.
Upon zone in, you hear Mograine shout:
"Bow down! Kneel before the Ashbringer! A new dawn approaches, brothers and sisters! Our message will be delivered to the filth of this world through the chosen one! "
 
Click play to view what happens in Scarlet Cathedral!
Once the sword is acquired, equipping it will curse the owner, turning the Argent Dawn faction to Hated (temporarily). However, visiting the Scarlet Monastery with the sword equipped yields interesting results! All the NPCs in the Cathedral instance will turn and bow before the person who has the sword. After you reach the Cathedral and talk to Scarlet Commander Mograine, the ghost of Highlord Mograine, the Ashbringer, enters and speaks with his son.

"Renault..."

"Father... But... How?"

"Did you think that your betrayal would be forgotten? Lost in the carefully planned cover up of my death? Blood of my blood, the blade felt your cruelty long after my heart had stopped beating. And in death, I knew what you had done. But now, the chains of Kel'Thuzad hold me no more. I come to serve justice. I AM ASHBRINGER."

"Forgive me, father! Please... "

<The Ashbringer smites his trecherous son with a blast of light.>

"You are forgiven..."