Along with Silas Wegg and Bradley Headstone, Mr. Fledgeby is one of the serious villains in this book. He is a moneylender, for starters, which means that he loans people money and expects them to repay him at a huge interest rate or he'll force them into bankruptcy. When it comes to explaining the source of Fledgeby's greed and cruelty, the narrator insists that it all comes from Fledgeby's feelings of inadequacy over the fact that he can't grow proper facial hair:
Young Fledgeby was none of these. Young Fledgeby had a peachy cheek, or a cheek compounded of the peach and the red red red wall on which it grows, and was an awkward, sandy-haired, small-eyed youth. (7.4.70)
Hmm, so because Fledgeby can't grow a mustache to twirl like a cartoon villain, he acts like a cartoon villain instead.
Throughout the book, Fledgeby looks at other men's beards and gets jealous, and he takes out his anger by calling in people's debts and causing them to fall into financial ruin.
The worst thing about Fledgeby is the fact that he won't take personal responsibility for the crummy things he does to people. Instead, he hires an old man named Mr. Riah to be the public "face" of his money-lending business and to make people think that Riah is the true villain. For his part, Fledgeby will never tell anyone how he makes all his money. And in Dickens' eyes, this makes Fledgeby even worse:
Fledgeby deserved Mr. Alfred Lammle's eulogium. He was the meanest cur existing, with a single pair of legs. (7.5.1)
Wow, Dickens. Tell us what you really mean.
Luckily, Fledgeby gets found out by the end of the book. Alfred Lammle beats him up (and stuffs pepper up his nose) and Jenny Wren puts even more pepper in his bandages. Still, though, you wonder whether Fledgeby gets off easily, considering the pain he's caused so many people.