The Black Prince is the ghost of a human man.
One of the "Happy Haunts" residing in the Haunted Mansion, the Black Knight's ghost dwells in one of the Changing Portraits, which flashes between his human form and a fierce, electrified, skeletal ghost-knight.
He was one of the knights who joined King Richard the Lionheart on his crusade, but refused to turn back from the gates of Jerusalem when the King ordered a retreat. His bloodthirstiness was punished by a freak bolt of lightning which vaporized him and his horse after it caught the tip of his raised sword. His ashes were brought back to England, where the portrait which would later make its way to Gracey Manor was painted, supposedly with his ashes mixed in the paint — hence why his spirit continued to haunt the painting.[UNOFF]
In 2015, during the Sea Captain's occupation of the Mansion, the Black Prince sided with him, taking charge of an army of several other Changing Portraits. Despite his generally unpleasant disposition, the Prince has been known to wander out of the Mansion with a drink in his skeletal hand.
The Black Prince first appeared as a part of the Haunted Mansion attraction in Disneyland, which opened in 1969.
A common interpretation of the Prince among fans is that he is intended to be the ghost of Sir Edward of Woodstock, who was referred to as the Black Prince. This, however, is unconfirmed.