What is "mercutio"

Mercutio 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, being neither a Montague nor a Capulet, Mercutio is one of the few in Verona with the ability to mingle around those of both houses. The invitation to Capulet's party states that he has a brother named Valentine.