John is the first character to whom we are introduced in "The Miller's Tale." We learn that he is a well-to-do carpenter who lives in Oxford, has married a much younger wife, and rents a room in his house to scholars.
When Nicholas locks himself in his room, John is very concerned about him and performs an "exorcism" on him.
John believes Nicholas's story about an impending flood and takes his advice about how to prepare for it by buying three tubs, stocking them with food, and hanging them from the rafters of his house.
John climbs into his tub the next night, only to hang there alone and fast asleep, while Nicholas has sex with his wife in their marital bed.
When John hears Nicholas shout "Water!" he thinks the flood is upon them and cuts the rope attaching his tub to the ceiling, taking a nasty fall.
The townspeople gather around the fallen John and mock him. All the clerks in the town say he is "wood," or crazy.