No, First Mate Cox and the Mutineers isn't the hottest new band to sweep the Caribbean. (We wish.) They're actually a pretty nasty bunch of men who spread death and destruction—and First Mate Cox is the worst, not just because he's nasty but because he's smart.
We first hear of First Mate Cox when Daphne is thinking about him after her shipwreck. And it's not too flattering. She remembers him telling her about calenture, "a special kind of madness, brought on by the heat" (1.4). Useful info, right? Well, except that he told her "probably hoping to frighten her because he was that sort of person" (1.4). You mean the sort of person who wants to terrify a 13-year-old girl traveling halfway across the world by herself? Sounds just the kind of guy you want to bring home to mom. Not.
First Mate Cox proves that the scariest men are the civilized ones. Daphne's father is initially afraid that some of the island men may have hurt her, but it's Cox and his men from England who come closest to doing so.
"He was the kind of weasel who would kick a corpse, because it was unlikely to fight back." (11.189)
First Mate Cox isn't just the kind of guy who would terrify a scared young girl. He's also the kind of man who would shoot the body out of a butterfly, shoot a helpless man in a canoe, "kick a corpse, because it was unlikely to fight back" (11.189)—and shoot a dolphin.
In case you forgot, Mau's people believe they become dolphins after they die. That's right: First Mate Cox kills souls.
He does this in more ways that one. When talking about Captain Roberts, Daphne says, "[Cox] wanted to shoot him in the faith" (11.202). In other words, he can't stand that other people have beliefs that he doesn't hold. Contrast that to Mau, who has also rejected his ancestral gods—but doesn't try to convince other people to his way of thinking. Basically, First Mate Cox is such a bad guy that his rebellion is doomed from the start.
Cox's followers Foxlip and Polegrave are just as bad—but they're stupid. Well, not too stupid to realize that they're better off sticking close to Cox than trying to fight him: "There are fish that swim alongside a shark, or even in its mouth, where they are safe from other fish and never get eaten" (11.190).
You've heard the term 'bottom feeders'. This is like that, but worse. But what can you expect from a man like Polegrave whose nickname is "Septic"?
These two call Daphne "princess," not as a sign of respect—no one knows that she's a princess yet—but to make fun of her. It's a "baby name" (11.28). And that sums up the mutineers' strategy, conscious or not: to make people feel less than they really are, just like Cox.
And, guess what? That strategy of treating people like they're idiots does the mutineers in. Daphne tries to get Foxlip to sing the song that turns the beer from being poison, but he refuses to sing "pagan mumbo jumbo" (11.94). Bad move, Foxlip. It kills him.
Cox himself meets a similar fate, letting his cockiness be the end of him. He thinks his gun will save him, but Mau's smarts win out. Strangely, Cox grins when he dies by axe and falls into the sharks below. Maybe he's happy to finally be with his own kind.