In 'Romeo and Juliet', Romeo's friend killed by Tybalt is Mercutio.
Mercutio is Romeo's close friend and a kinsman of Prince Escalus, which lets him move between Verona's rival Montague and Capulet circles. He is witty, provocative, and famous for his imaginative Queen Mab speech in Act I.
The crucial confrontation occurs in Act III, Scene 1. Tybalt challenges Romeo, but Romeo refuses to fight because his secret marriage to Juliet makes Tybalt his kinsman. Mercutio is enraged by what he sees as Romeo's submission and takes up the duel himself. Romeo tries to intervene, but Tybalt reaches Mercutio beneath Romeo's arm and mortally wounds him.
Mercutio's death marks the play's sharp turn from comedy toward tragedy. His dying curse—“A plague o' both your houses!”—condemns both families. Romeo then kills Tybalt in revenge, leading Prince Escalus to banish Romeo from Verona. A common mix-up is to say Romeo kills Mercutio; Romeo is responsible for the intervention that exposes him to danger, but Tybalt delivers the fatal wound.