Final answer:
The mummer in Poe's 'The Masque of the Red Death' is a symbolic representation of the plague, whose appearance brings the story to its tragic end.
Step-by-step explanation:
The mummer in Edgar Allan Poe's The Masque of the Red Death is a mysterious figure that arrives uninvited at Prince Prospero's masquerade ball. The presence of this figure, who is dressed to represent the deadly Red Death plague, instills fear among the guests. The mummer's unsettling personification of the Red Death ultimately catalyzes the story's tragic conclusion, where all the partygoers, including Prince Prospero himself, succumb to the plague.
Mummers' plays, which the question references, are a form of folk drama that originates from England and Ireland. These plays often involve a symbolic combat between characters, followed by a resurrection brought about by a doctor character, signifying themes of death and rebirth that are paralleled in Poe's story.