From the in-game description:
Quote:
The Headless Horseman, once a knight of the Silver Hand and hero among his fellow paladins, is cursed. Driven insane within the Scarlet Monastery, he believes that he is alive and we are dead. Now, his fervor no longer serves the Light. With the coming of Hallow's End, he spreads gloom and fire across the villages of Azeroth.
Check out http://www.wowwiki.com/Headless_Horseman for more info.
