The castle Hall at Christmas always had some theater productions. Traveling players may have been engaged to put on shows (Christmas was a time when any and all jongleurs and singers could count on picking up work if they didn’t mind sleeping in the corner of the hall or perhaps the dog kennels). But there was a long tradition in England for amateur local drama at this season. It seems clear that the winter/spring drama tradition went back well before conversion to Christianity and probably had its roots in some kind of death/rebirth metaphor for winter and spring. Its themes had ceased to make any sense to anyone; they were traditional, that was enough.
Local amateur holiday actors were called Mummers because they “kept mum” about their real identities, always wearing masks or other costumes. We know from medieval paintings that they often wore animal heads, like deer and foxes. At the same time, we know that the traditional story they told wasn’t about wearing animal heads–so it’s not clear how they put it together. The traditional story began with a presenter who might be a Fool, the Devil, or Old Man Winter. An anti-hero showed up with a ranting versified challenge, and the presenter called for a champion, who duly versified. Then they fought with swords, and the anti-hero died. Next, a doctor came out and had some method to bring the anti-hero back to life.
By the time we have clear records of the Mummers, the story was clearly influenced by the Crusades, which neatly provided a Muslim anti-hero. By the 18th century, the Muslim was specifically a Turk, though in the Middle Ages proper this was pretty unlikely since the Turks did not become part of European consciousness until the fall of Constantinople and, later, their attack on Vienna. The hero was nearly always St. George the Dragon-Slayer, and the presenter became Father Christmas. Local groups could put their own satirical patter into the story, and they could plan their own variations of staging. Bit parts could be added for comic relief.
During Christmas season, Mummers went from house to tavern to house, and eventually to the castle or bishop’s palace. At each place, their lead character walked in and commanded attention with his first speech. The audience knew what to expect, but waited to see if there were any fresh twists put into the familiar narrative (they also didn’t hesitate to heckle and call out their own punchlines). By the time show was over, all characters had entered the room to play their parts, and the “fight scene” was often a choreographed dance. Some characters might sing additional songs, and they closed with a dance while one or more of them circulated among the crowd with a donations box. Mummers were fundraisers; sometimes they were guild members, and later they were members of a club raising money for a charitable or public project.
There’s a record of mummers playing before Richard II during the post-plague years, around the time of the Peasants’ Rebellion. Christmas Day had passed and it was the Feast of the Epiphany, the traditional day to remember the visitation of the Magi. The players who entertained the king were elaborately costumed to represent the Pope, cardinals and African princes. They played out a game of dice with the king (with loaded dice to make sure he won) and then presented him with gifts. Another late medieval mummery that left records was in London; the goldsmiths’ guild put on a show dressed as King David and the 12 Tribes of Israel.
Mummery became a problem for law enforcement because during Christmas season, nobody asked questions of a man in an antlers or Devil mask wandering the town at night. It was too easy to get drunk and start trouble, or to pose as a Mummer and rob houses while they danced. The church kept up an official attitude of disapproval for Mummery and town officials did their best to keep it restricted to approved groups.
Modern mummery examples here and here and here. The last one has a Turkish knight and adds bit parts like a “King of Egypt,” a cross-dressing “Princess,” and a Dragon.