Pyrocles and Cymochles are a real nuisance in Book 2. Pyrocles, whose name means "troubled with fire," is constantly looking for fight and stirring up trouble for its own sake. His brother, Cymochles, whose name means "trouble with waves," is constantly lounging around, doing nothing much, occasionally trying to save him bother.
Together, these two brothers represent opposite ways of being weak-willed and intemperate (remember, temperance is the theme of Book 2): either by not checking your desire for action, or having pretty much no desire for action to speak of (although, to be fair, Cymochles does act, so it's not a perfect correspondence). The fact that they're both killed by Arthur after they refuse to pardon Guyon shows that their inability to control their extreme inclinations is ultimately self-destructive.