Oh, John Aycliffe is so horrible. Seriously, dude doesn't give us one thing to like. He is the steward of Lord Furnival's manor of Stromford, which means he's the law of the land in the absence of Lord Furnival. And because Lord Furnival is literally never there, Aycliffe lives in the manor house and is always the top guy in charge. And he's a jerk. Think the Sheriff of Nottingham, only worse.
No one ever accuses John Aycliffe of any kindness. In the absence of Lord Furnival, he is in charge of the manor, the laws, and the peasants. And under his watch, getting caught in some small transgression—missing a day of work, speaking harshly of his rule, failing to attend mass—brings an unforgiving penalty. It could be a whipping, a clipping of the ear, imprisonment, or a cut-off hand. For poaching a stag, John the ale-maker's son was put to death on the commons gallows:
As judge, jury, and willing executioner, Aycliffe had but to give the word, and the offender's life was forfeit. We all lived in fear of him. (1.13)
Yikes, right? Aycliffe is the unquestioned villain of the novel. While we know that Lord and Lady Furnival are not the world's greatest people, Crispin never comes in direct contact with either of them, so they remain bad guys at a distance. Aycliffe is the one who has made Crispin's life miserable from birth, though, the one who accuses him of theft and murder and proclaims him a wolf's head, the one who pursues him all the way to Great Wexly and does his best to kill him, and then in the end tries to break his oath to let Crispin and Bear go. As a bad guy, Aycliffe just won't quit:
His gaze showed such disdain, I could feel my wrath rise within. Here was the man who had been so cruel to my mother. Who had treated me with such contempt and wished me dead. Who had murdered Father Quinel. Who had abducted Bear. (56.3)
There's one teensy glimmer of hope in Aycliffe, and that's that he does all this for Lady Furnival, who's a relative of his. If it were known that Lord Furnival had other heirs, her inheritance would be in doubt and she'd be in big trouble. Aycliffe is doing his darndest to make sure this doesn't happen. It is a teeny-weeny sliver of hope, though, because it could be that Aycliffe is only trying to help Lady F in hopes of getting a share of that inheritance for himself, too.
See? We tried to give Aycliffe some sort of not-entirely-evil-and-self-interested motivation, but it's doubtful. The guy just never shows any kindness at all, so he only has himself to blame.