The Masque of Red Death: a short story by Edgar Allan Poe about some village being ravaged by an unknown plague and all it's nobles lead by Prince Prospero hide away in a church and party like there's no tomorrow while the peasantry die off until one midnight a mysterious figure in a red robe and mask invades their party and ultimately kills everyone by simply being there.
In 1964, there was a film adaptation where the Red Death and Prince Prospero were both played by Vincent Price. Other added twists were Prince Prospero being a Satanist and other colored deaths representing other deadly diseases appear near the end of the movie, I may post those pictures if I get enough faves here.
©Whoever made the film