Davy Prentiss Jr. is the brat kid of Mayor Prentiss. He's first described as "Mr. Prentiss Jr. The man of the law" (4.42), but what we find out through the course of events is that he's really just his daddy's pawn. He does his father's dirty work, but he doesn't really have much in the way of his own spark of evil genius.
Don't get us wrong—he's still a bundle of nasty. We really see this when Todd and Viola come across him in the woods and he busts out this gem: "But that's the lesson you learn, eh? Dogs is dogs and women turn out to be dogs, too" (23.69). Ah yes, the apple doesn't fall far from the tree.
Let's not overlook the fact that he's also really young. Todd describes that "he ain't barely two years older than me, barely able to even get a sentence out without his voice breaking" (4.72). But of course in Prentisstown, he counts as a man because he's technically of age and has completed the requisite becoming-a-man murder. In this way, then, he's a bit of contrast to our main man, Todd, who might be grumpy, but is a glowing example of humanity next to this twerp.