Thomas Cromwell is so nasty that we're pretty sure that he's Martin Shkreli's ancestor. He's so evil that he might be related to Emperor Palpatine. And we hate to get straight up slanderous, but we're pretty sure that he listens to Nickelback, too.
Okay, that's too far, we know. But you get the point right? Dude's bad.
First off, Cromwell is the shadiest politician in the game. Think of him at the corrupt backroom lobbyist of 16th-century England, exploiting the law and using unsavory means to reach his power-hungry goals. If you don't believe us, just check out Crommy's opinions on the law and what you can do with it:
CROMWELL: [...] You're absolutely right, it must be done by law. It's just a matter of finding the right law. Or making one. (2.232)
Now contrast this perspective with that of good old Thomas More, who treats the legal system with a sanctity that most people reserve for their Higher Power:
MORE: The law is not a "light" for you or any man to see by; the law is not an instrument of any kind. (2.714)
Yeah, it's like night and day. In fact, it's More's total devotion to the law that makes him such enticing prey for a big-game hunter like Cromwell.
Unfortunately, Cromwell isn't merely a shady politician—he's pretty much a bona fide sadist. Think back to when he shoves Rich's hand into a candle during one of their early meetings just for kicks. Or think about when he strolls through the Tower and eyes its range of torture equipment with a very creepy glimmer in his eyes. He seems to take real glee in hurting people.
In fact, one thing that sets Cromwell apart from the other characters in this play is his sociopathic belief that he is somehow above the law, that he is somehow so superior to everyone else that none of the rules apply to him. He doeesn't care about hurting other people, because to him, they're nothing. The only thing that matters for Cromwell is number one.
So what are we to make of this force of evil standing the victor at the end of the novel? Well, don't get too concerned—as Common Man notes, Cromwell himself will eventually get executed for treason. That's the very definition of poetic justice.
Regardless, Cromwell's unchecked rise to power shows us the overwhelming nature of corruption, and More's hopelessness in fighting it.