A reader can interpret the title of Edgar Allan Poe's story of a masque as a disguise--the "disguise of Red Death," the guest who enters and really is his disguise--or as the party that is called a masque, or a "masquerade of the Red Death."
Thus, the Red Death is the secret guest who becomes his costume, while also being the one who generates the masquerade party. In either case, he it is who controls the celebration of the revelers; the Red Death is inescapable. This is Poe's message about death: Nothing can keep it away; death controls life.
Masquerades were popular in Venice during the Carnival season in the fifteen century. In the eighteenth century masquerades were held in London and involved elaborate costumes which hid the identity of the guests. These masques gained a reputation for unseemly behavior, unescorted women, and even anonymous attacks upon people, attacks that were sometimes fatal, such as assassinations of unsuspecting prominent officials.
Just as the guests of these libertine masques often felt themselves safe in their costumes and revelries only to be attacked or exploited, the guests of Prince Prospero find themselves confronted by the Red Death who has made his entry "disguised" as himself in order to control all the guests.