Mercutio is a foil to Romeo. This means his personality is meant to contrast with Romeo's. Where Romeo is love-sick, love-struck, a romantic, and impulsive as a result, Mercutio is just the opposite. He is quick witted and makes fun of love. He is generally level-headed, rational and realistic. He does not have a love interest and makes fun of Romeo's silliness in that area. Even when he fights (to his death) he is more than provoked before he joins. And at first, he almost joins jokingly. When the fight turns serious is when he gets mortally wounded. His final words are "A plague on both your houses!" This is as if to say, your love for each other was not worth dying for.