Answer: Mercutio (/mərˈkjuːʃioʊ/ mər-KEW-shee-oh,[1] Italian: Mercuzio) is a fictional character in William Shakespeare's 1597 tragedy, Romeo and Juliet. He is a close friend to Romeo and a blood relative to Prince Escalus and Count Paris. As such, Mercutio is one of the named characters in the play with the ability to mingle around those of both houses. The invitation to Lord Capulet's party states that he has a brother named Valentine.
Though often fun-loving and witty, the latter demonstrated in his Queen Mab speech in the first act, Mercutio's sense of humour can at times be facetious or even coarse, much to his friends' annoyance. He is also moody and given to sudden outbursts of temper, one of which sets a key plot development in motion.
In the story, he was a close friend of Romeo. Earlier versions of the story described a different chain of events leading to Tybalt's death, omitting Mercutio completely. Arthur Brooke's The Tragical History of Romeus and Juliet and William Painter's 1567 versions of the story both left the entire episode solely to Romeo and Tybalt. In both stories, Tybalt attacks the pacifist Romeo with such force that Romeo is forced to take up the sword to defend himself. He is then banished rather than executed because the killing was provoked. In 1672, English poet John Dryden wrote, "Shakespeare show'd the best of his skill in his Mercutio, and he said himself, that he was forced to murder him in the third Act, to being killed by him."[5]
The addition of Mercutio into the fray increases the tension, and Tybalt is seen as a slightly more peaceful character than in previous versions, as Mercutio is disgusted by the fact that Tybalt continues to search for a quarrel with Romeo, when Romeo is trying to bring peace between them. Mercutio hurls insults and taunts at Tybalt, and draws the sword first, in reaction to Tybalt's insults, which are directed to Romeo.
Mercutio's death in Act III, scene I is the pivotal point of the play, which up to this point is relatively light-hearted.[6] Mercutio's death is sudden and makes death a dark reality for several characters, causing a domino effect of tragic fate that leads ultimately to the tragic climax.
This has been taken from WIKIPEDIA _ https://en.wikipedia.org/wiki/Mercutio