Romeo, who Tybalt means to challenge to a fight.
Tybalt's uncontrollable vengeance
Friar Laurence
Benvolio and Tybalt was there at the scene with Romeo when Mercutio was stabbed; then died.
That he is a skilled swordsman.
Benvolio urges tybalt and mercutio to take their fight off the streets because there are people watching and the prince would get them in trouble if he saw them fighting.
Benvolio (in Act 1), Mercutio and Romeo (in Act 3).
Benvolio encourages Mercutio to stop fighting with Tybalt. He tries to restrain Tybalt without any success.
Mercutio does. It's ironic because Benvolio is peace-loving and it it Mercutio who has the quarrelsome temperament.
Benvolio informs the Prince that Tybalt killed Mercutio, and in retaliation, Romeo killed Tybalt. He explains that he tried to separate them, but Tybalt provoked the fight leading to the tragic events.
It will start a war.
Benvolio tells Mercutio to retire because he senses a brewing confrontation between Mercutio and Tybalt, and wants to avoid any violence. Benvolio is concerned for their safety and tries to diffuse the situation by suggesting they leave.
Benvolio isn't more important than Mercutio. Benvolio is a good friend to Romeo (Benvolio sort of means 'well-meaning' in street-Italian), but he doesn't make much difference to the plot. Mercutio picks the fight with Tybalt that turns this from a lovestory into a tragedy. Benvolio tries to joke Romeo out of his pash on Rosaline, tries to persuade Mercutio not to fight Tybalt, tries to get the Duke not to banish Romeo - but nobody ever listens to Mercutio. A nice fellow - but not a lot of use to anybody.