John and Aleyn are two clerks (students) from a college in Canterbury that has its wheat ground into flour at Symkyn's mill. When Symkyn takes advantage of the college manciple's illness to cheat the school of some of its flour, these two clerks travel to the mill the next time the school needs its flour ground, in order to make sure Symkyn doesn't steal any this time.
John and Aleyn are pretty confident – some might say overconfident – that "the millere sholde not stele hem half a pekke / Of corn by sleighte, ne by force hem reve" (156-157). In fact, they "leye hir nekke," or swear it on their lives (155). The fact that they can't imagine that Symkyn might be able to cheat them, despite his tricking of people much older (and probably wiser) than them, suggests that these two possess the overconfidence of youth – a feeling of invincibility that comes from a lack of experience of life's hard knocks. The narrator tells us that these two are "testif," or headstrong, a characterization that confirms our suspicions (150).
In addition to being headstrong, John and Aleyn are "lusty for to pleye" – eager to have a good time (150). The narrator tells us that their motivation for wanting to go to the mill is not a deep concern for the school's finances, but "oonly for hire mirthe and revelrye" – to have a good time (151). You can just imagine these two fist-bumping and crying, "Road trip!"
Of course, when they get to the mill, Symkyn's trickery ruins their fun when they have to spend most of the day chasing down their escaped horse. This "il fit," or evil time they've had, is one reason Aleyn thinks he's entitled to have sex with Symkyn's daughter. By doing this, he hopes to get the "pleye" he's been hoping for, as well as to gain "esement," or compensation, for the corn Symkyn has stolen from them. Later, John gets on board with this plan as well by sleeping with Symkyn's wife. By taking their compensation in the "pleye" of sex, John and Aleyn reveal themselves to be motivated mainly by their desire for "mirthe and revelrye." Just like it was with their request to be allowed to travel to the mill, their cry for justice and fairness is just a cover for their true motivation.
Both Aleyn and John are from the same town far in the north of England, a place called Strother. The narrator isn't even sure of the town's location, so it's probably a small place. The two speak in a northern accent, replacing the o's in their words with a's (for example, saying "bathe" instead of "bothe") and using words from their regional dialect that might have been unfamiliar to people from other parts of England. Their speech is the first example in English of a writer trying to imitate a dialect other than his own.
As students in a university, Aleyn and John come from an educated class. The tale contrasts the clerks' elite class with that of the miller, who is part of the uneducated tradesman's class. No one is more aware of this distinction than the miller himself, who seems to take their learnedness as a challenge, declaring "yet shal I blere hir ye [cheat them], / For al the sleighte in hir philosophye" (195-196). He makes clear a rivalry between himself and these more educated clerks, which mirrors the one that occurs between John the carpenter and Nicolas and Absolon in "The Miller's Tale".
Another way in which John and Aleyn resemble Nicolas and Absolon from "The Miller's Tale" is as paired characters who are virtually undistinguishable from one another. The Miller, in turn, created Nicolas and Absolon in answer to the characters of Palamon and Arcite in "The Knight's Tale." John and Aleyn, then, are the third such grouping we see in as many tales.
Like those earlier pairings, the "arc" of John and Aleyn's story revolves around an attempt to possess a woman or women. In "The Knight's Tale," the two men's love for their object of desire is couched in terms of noble, courtly love. In "The Miller's Tale," the love for the woman becomes mere lust. In "The Reeve's Tale," the sex has descended from the joyous, life-affirming act it was in "The Miller's Tale" to a violent, brutal act of revenge.