Sir Thomas Thomson aka Sir Thomas <Son of Thomas> (better known as the Headless Horseman) was once a Knight of the Silver Hand and hero among his fellow paladins. He became cursed, driven insane within the Scarlet Monastery, and believed that he was alive and that everyone alive was dead. His fervor no longer served the Light. With the coming of Hallow's End, he spreads gloom and fire across the villages of Azeroth.
He appears in his true but ghostly form after his headless form is defeated. He then asks for forgiveness, and that his holy tome, the Tome of Thomas Thomson be brought back to a Costumed Orphan Matron.
In one these raids however, he accidentally killed his own family before he realized it was them. He came to the conclusion that a storm destroyed the last ship fleeing to Kalimdor, and all the workers have either been drafted into service or became one of the undead themselves and thus had to hide wherever they could. Broken, he was taken back to the Scarlet Monastery where he finally went mad, believing the entire world to be infected and he alone was the only being that could save them. After killing many of his former comrades, he was beheaded. Dathrohan decided to give the fallen crusader a honorable burial. Once entombed, Dathrohan (who in truth was Balnazzar disguised as the fallen general) warped Thomas' corpse into becoming a death knight, thus creating the Headless Horseman.