The Black Cauldron is the titular object of The Black Cauldron. Fueled by the spirit of the dark lord Arawn, who was once an evil overlord, who ruled over the land of Prydain. During the prologue, the narrator talks about the history of the Black Cauldron and how the overlord came to become it.
The Black Cauldron
As stated in the prologue: "Legend has it, in the mystic land of Prydain, there was once a king so cruel and so evil, that even the gods feared him. Since no prison could hold him, he was thrown alive in to a crucible of molten iron. There his demonic spirit was captured in the form of a great Black Cauldron."
The face of the overlord is apparently engraved upon the cauldron. At certain points in the movie, the face is illuminated.
For uncounted centuries the cauldron remained hidden while evil men searched for it, one of these men was a wicked emperor known as the Horned King who seek to find the cauldron and use it's power to unleash an army of deathless warriors.
Taran traded his Magic Sword for the cauldron in hopes to destroy it, but was told by the Witches of Morva the Black Cauldron was indestructible. However, all of the Black Cauldron's evil powers could be undone if a soul willingly climbed into the cauldron at the cost of their own life. Taran's choice to find the cauldron was his biggest mistake when he and his companions were captured by the Horned King's guards. With the cauldron in his possession, the Horned King brought his Cauldron Born army to life and sent them to conquer all of Prydain.
Taran attempted to sacrifice himself by jumping into the cauldron but Gurgi made the sacrifice himself, as a result all of the cauldron's evil was undone, killed the Horned King and destroyed the castle.
The cauldron was last seen floating in the water where Orddu, Orwen, and Orgoch were waiting to take it but not before they bargined with Taran to return Gurgi.
In the House of Mouse episode, House of Magic, Daisy Duck accidentally makes the House of Mouse audience disappear. When they ask the Magic Mirror for help, he tells them to check the prop basement for something magical to help them. Daisy and Minnie find the Black Cauldron (a sign on it says: Who So-Ever Uses the Black Cauldron for Evil Will be All Powerful), and decide it's what they need.
Daisy dresses as Maleficent and attempts to cast a spell. She ends up summoning the Cauldron Born instead. In order to make it go away, she casts a spell. However, in the process, she makes the whole House of Mouse disappear. After everything was set straight by Jafar, Daisy attempts to use the Cauldron as a fondue pot, again summoning the Cauldron Born.
A cauldron similar to the Black Cauldron appears in this direct to DVD feature. However this cauldron is in the possession of The Evil Queen and talks to her via magic. Each time it talks, it speaks in a male voice and tries to give ideas for the Queen. The first story told explains how this particular cauldron ended up in the Queen's dungeon, which links it back to the Black Cauldron.
Behind the scenes
The idea of an evil overlord ruling Prydain is not unfamiliar to the source material. In the books that the Black Cauldron was based on, the overlord is named Arawn, the Deathlord of Annuvin. Arawn was originally to be the main villain of the Black Cauldron, just like in the books. However, Arawn was replaced by the Horned King because animators felt that audiences would like Horned King better because he had horns. Several people working on the film were discouraged about this because they had read the books and felt that you couldn't do the film based on the book without the book's main villain. It is implied that the Spirit of the Cauldron is actually that of Arawn, but is unconfirmed.