The Black Prince refers to one of the changing portraits at Disneyland, Walt Disney World, and Disneyland Paris, as well as to the character depicted therein, whose ghost presumably haunts the portrait. He is notable for being the only formally-identified real, historical ghost in the Haunted Mansions at Disneyland and Disneyland Paris.
The portrait shows a fierce knight on horseback that rots away into a monstrous skeleton wraith (some fans interpret the painting slightly differently, saying that the prince is being struck by lightning rather than progressively decaying). In the portrait's original six-part version, the decay would have been progressive, beginning with the armor visibly rusting.
The painting depicts the historic prince Sir Edward of Woodstock who during the 100 year war was known as the Black Prince. He was the first Duke of Cornwall, the Prince of Wales, and the Prince of Aquitaine. Edward was born on June 15, 1330 in Oxfordshire, England. He was a strong military leader and was very famous for his victories over France in battles of Crecy and Poitiers. He is most notorious however for his sacking of the french town of Limoges in 1370 in which he reportedly personally slaughtered over 3,000 men, women and children out of anger for having been betrayed by a friend who was native to the town. Edward died on June 8, 1376 from dysentery in the Palace of Westminster.
In the rides
When the Haunted Mansion at Disneyland opened in 1969, this painting was the second one down on the right side of the gallery. It flashed back and forth between knight and skeleton in sync with the lightning, but when the effect was discontinued, he slowly faded back and forth between images. In 2006, when the effect was redone again, Edward's portrait survived and still flashes between knight and skeleton.
Walt Disney World
The portrait of the Black Prince was added to the Walt Disney World Portrait Corridor in 2007. He is the third painting down the hall, and like at Disneyland, he flashes between knight and skeleton with the lightning.
In Disneyland Paris's Phantom Manor, the Prince's portrait used to hang in the Portrait Corridor, slowly transforming between knight and skeleton. This was removed during the 2019 refurbishment. The Phantom Cowboy portrait however seems to be inspired by the Black Prince portrait.
In issue no. 1 of the Disney Kingdoms Haunted Mansion comic, the Black Prince (called the Horseman in the comic) is the leader of the portrait monsters that work for the Captain. He chases Danny through the Mansion, threatening him with his sword, and interestingly quoting some of the Ghost Host's dialogue as he does so. Constance decapitates him before he can tell the Captain, rendering him powerless.
The film adaption has a similar portrait, except the same effect is applied to the famous historical painting of Napoléon Bonaparte on horseback, as opposed to the Black Prince.
As with the other changing portraits from the film, the portrait wasn't originally featured in the film. They were added in as testing audiences voiced their disdain for the film so they shot certain scenes in-order to directly reference the ride as a means of trying to make the film more tolerable for audiences.