Benvolio, a member of the Montague family, establishes himself as a peacemaker in Act 1. Primarily, his name suggest that he is a good person, as "ben" is a Latin root meaning "good." During the brawl with the Capulets, Benvolio attempts to stop the fighting. When he is provoked by Tybalt, Benvolio says, "I do but keep the peace. Put up thy sword,/ Or manage it to part these ment with me" (1.1.68-69). In response, Tybalt scoffs at Benvolio's statement, saying, "What, drawn and talk of peace? I hate the word/ As I hate hell, all Montagues, and thee" (1.1.71-72). Clearly, these two characters are foils for each other, as their behavior is markedly different.
Romeo's secret behavior stems from his love for Rosaline, a woman who will not return this affection.
A cousin and friend of Romeo's, Benvolio is usually the voice of reason for the more emotional Romeo. In Act I, he judiciously tells the street brawlers,
Put up your swords; you know not what you do. (1.1.54-55)
After Lord Montague rushes out to the street, Benvolio offers him a calm, rational, and blameless explanation of the situation, telling him that the Capulet servants were fighting with theirs when the fiery Tybalt Capulet entered and wielded his sword against him. Benvolio adds that they were only exchanging "thrusts and blows...Till the Prince came" and parted them. Then, when Romeo's father asks about his son's whereabouts, Benvolio replies that he has seen Romeo wandering in the Sycamore grove, but does not know the reason he shuns company. After Benvolio promises Lord Montague that he will learn what troubles Romeo, Lord Montague then exits.
When Romeo approaches, Benvolio stops him and with great solicitude he inquires about the cause of Romeo's melancholy. Romeo finally reveals that he is "out" of love as the woman does not love him. In an effort to cheer Romeo, Benvolio makes light of what he has said,
Alas, that love, so gentle in his view,
Sould be so tyrannous and rough in proof! (1.1.159-160)
But, when he realizes that Romeo is truly despondent, Benvolio sympathizes, saying that he "rather weep" at Romeo's "good heart oppression" (173-175). Further, he tries to cheer Romeo by teasing him. For instance, when Romeo tells Benvolio that the woman he loves is beautiful, Benvolio becomes a little bawdy: "A right fair mark, fair coz, is soonest hit" (1.1.198). But, when Romeo remains despondent, Benvolio suggests that he look elsewhere in order to forget about his unrequited love; there is a feast at the Capulet's where "admired beauties of Verona" will be.
But in that crystal scales let there be weigh'd
Your lady's love against some other maid
That I will show yon shining at this feast (1.1.98-100)
A volatile cousin of Juliet, Tybalt has an irrational hatred for the Montagues. (In Luhrmann's 1996 film, Tybalt enters dressed in a devil's costume.) His first words display well his choleric temperament as he accosts Benvolio:
What drawn, and talk of peace? I hate the word
As I hate hell, all Montagues, and thee:
Have at thee, coward! (1.1.56-58)
Tybalt does not reappear until Scene 5 when he spots Romeo at the feast. When he does, he immediately calls for his sword as he is incensed that Romeo would dare to come wearing a mask--"an antic face"--and "scorn our solemnity" (1.5.55). Because his character is one of loyalty (recall his impassioned defense of Juliet and the family), Tybalt feels justified in killing Romeo: "To strike him dead, I hold it not a sin" (1.5.61). His anger grows as he informs his uncle that a foe has come to "scorn at our solemnity this night" (1.5.65). Lord Capulet tells him to leave Romeo alone because the time is wrong: "You'll make a mutiny among my guests!" (1.5.79). Tybalt agrees to withdraw, but Romeo's prank will be paid for later.
I will withdraw, but this intrusion shallNow seeming sweet, convert to bitterest gall. (1.5.90-91)
Benvolio is the peacekeeper while Tybalt is the tyrant (haha, is sound the same). They are together to show each other's characteristics. Benvolio seem even more innocent next to Tybalt as Tybalt seem more violent next to Benvolio. Also, Romeo's secret behavior is due to his love to Rosaline. At least, only durring the time his father/Benvolio mention it.