Tybalt, a short-tempered young man, was the son of Lady Capulet's brother and Juliet's first cousin. He was also Romeo's rival. Mercutio often called Tybalt "the prince of cats" because of his sleek, yet violent manner.
Tybalt: I am Tybalt, the prince of cats! I am short-tempered and violent, and I am always looking for a fight. If you cross me, you will regret it!