In Shakespeare's "Romeo and Juliet," in both Act Two and Act Three, Mercutio refers to Tybalt as the "King of Cats." In Act One when Benvolio asks "Why, what is Tybalt?" Mercutio replies,
More than Prince of Cats, I can tell you. Oh, he's the courageous captain of compliments [expert in fashionable behavior]. He fights as you sing, keeps time, distance, and proportion; rests me his minim rest, one, two, and the third in your bosom. The very butcher of a silk button, a duelist, a duelist, a gentleman of the the very first house [finest school]. Ah the immortal passado! The punto reverso! The hai! [dueling terms] (II,iv,16-20)
Then, in Act Three, as Mercutio and Tybalt banter words, Romeo enters after having married Juliet. Tybalt insults Romeo, who tries to tell Tybalt that he can no longer hate him. But Tybalt calls Romeo a villain and challenges him while Mercutio pulls his sword and demands that Tybalt fight:
'Tybalt, you ratcatcher, will you walk?'
good King of Cats, nothing but one of your nine lives, that I mean to make bold withal and, as you shall use me hereafter.... (III,i,63-66)
Of course, the connotation of Cat is stealthy and sneaky, as well as skillfully treacherous--all of which are characteristic of Tybalt. Prince of Cats is an allusion to the story of Reynard the fox, a character known to Elizabethan audiences. Tybalt (Tibalt) is Prince of Cats in this beast-epic, popular in French, Dutch, and German literature. Reynard and Tibalt, along with others are all anthropomorphic animals in these fables who plot one stratagem or another.
I assume that you are talking about Scene 4 from Act II. In this scene, Mercutio and Benvolio are worrying about Romeo. He has gotten a challenge from Tybalt and they don't think he's up for the fight.
What Mercutio says about Tybalt is that he is a really good fencer. He talks about how Tybalt fights as easily as someone else would sing at a recital. He says that Tybalt knows all the important fencing moves.
So, it really doesn't say what kind of person he is in the sense of what his personality is like -- Mercutio is just talking about how dangerous he is.