The names of these two characters, which are introduced in actual spoken lines (not just speech prefixes or _Dramatis Personae)_ within the first two scenes, would largely have answered this question for an Elizabethan audience. Benvolio is Italian for _I mean well_ --cf. the word _benevolent._ Mercutio is the prime example of the _mercurial_ temperament in John Draper's _The Humors & Shakespeare’s Characters_ (Duke UP 1945, rpt. AMS 1965). A mercurial temperament is an unstable one in which each of the four humors prevails by turns.