The pirates that capture Captain Phillips after invading the Maersk Alabama are given quite classical roles in the movie, I think:
There is Muse, the voice of reason (compared to the others at least) and tactically-thinking leader.
Najee gives the aggressive and hot-headed opposite, who more than one time challenges Muse for his supposed softness.
And there is the young and overextended Bilal who gets injured and starts to sympathize with Captain Phillips.
(Elmi, the one steering the lifeboat, seems to stay rather under-developed compared to the other three, I think.)
But I wonder in which way those characters match their descriptions from Richard Phillips's book (which I admittedly haven't read). The Wikipedia article says that he portrays them as "alternately conciliatory, vicious, and unfocused". But it doesn't explain if he attributed those traits more to single characters or rather to the group as a whole at different times. Or maybe he didn't differentiate the various characters of the pirates in the same clear way the movie did. It would therefore be interesting to know in which way the movie differs from the book in its depictions of the pirates and what the reasons for those differences might be (if any).
(In fact I'd also like to ask if the pirates' characters match those of their real-life counterparts during the hostage crisis, but I see that apart from Richard Phillips there aren't really any witnesses for that.)