The Horned King is a fictional character from the fantasy series The Chronicles of Prydain, and in the film The Black Cauldron by Disney (voiced by John Hurt).
In the book series, he appears only in the first book, The Book of Three. He is Arawn's champion and the War Leader of Annuvin. The Horned King is described as a huge man wearing armor (except for his arms, which are naked and stained crimson), a red cape and an antlered skull mask. The antlers are presumably where he gets his name.
Arawn sends the Horned King to capture the pig Hen Wen from Caer Dallben. He follows Taran across Prydain in search of the oracular pig Hen Wen, but cannot find her. In the end, he marches his army to Caer Dathyl and attacks Taran when he and Eilonwy try to warn the Sons of Don of the impending attack. Taran tries to fight him with the sword Dyrnwyn, but is nearly slain by the sword's fire in his attempt to draw it. Gwydion is able to defeat the Horned King by speaking his true name, which is never revealed; upon the utterance of his name, the Horned King is struck by a lightning blast and consumed by flames, disappearing below the surface.