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.
Thomas Thomson was present as the Scourge destroyed Lordaeron. He witnessed Baron Rivendare's betrayal when he sent a large supply of plagued grain to a village he was defending. He received word that not only had Prince Arthas returned from Northrend and murdered his father, he would later murder Uther the Lightbringer. And finally the last great Paladin of the Silver Hand, Alexandros Mograine, the Ashbringer was slain. Desperate to keep his family safe, he ordered his wife to flee to Kalimdor while he remained in Lordaeron with the Scarlet Crusade to destroy the Scourge. However under Saidan Dathrohan's wing, Thomas, like so many Scarlets, became fanatical and saw everyone as being plagued and participated in many of their raids.
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.