What types of characters does Shakespeare include in Romeo and Juliet?
There are basically two sets of opposite characters in literature. There are both round and flat characters as well as dynamic and static characters. Round characters are well developed. The audience has a good idea of that character's traits. A flat character is simply that. We know very little about them and they are often included only for plot reasons. On the other hand, a dynamic character is not only one with well defined attributes, but that character also changes over the course of the story. A static character may also be well developed but doesn't change.
There are several round characters in Romeo and Juliet including Romeo, Juliet, Mercutio, Benvolio, the Nurse, Lord Capulet, Tybalt and Friar Lawrence. Each of these characters are relatively well developed. For example, Romeo is portrayed as impetuous in nature as he falls in love easily and could be considered courageous, both in his willingness to rebel against the parameters of the feud and in standing up for his and Mercutio's honor against Tybalt. Mercutio is defined by his humor and his arrogance which are often on display up until his death in Act III, Scene 1. Benvolio is good natured and a peacemaker. The Nurse is loving but sometimes lacks loyalty. Lord Capulet is conflicted as he both loves his daughter but is also willing to violently berate her when she doesn't yield to his will. Tybalt may not be quite so round, yet the audience is aware of his quick temper and willingness to do anything to honor his family and the code of the feud. Friar Lawrence is also conflicted. On one hand, he loves and supports Romeo and Juliet, but on the other, he sees that they are moving too fast and should display more patience in their love. All of these characters, however, should be considered static. They do not change over the course of the plot. Romeo is impetuous to the end. Mercutio is joking to his death and Friar Lawrence is still conflicted in his final speech to the Prince.
In my opinion, the only truly round and dynamic character is Juliet. She goes from an immature girl who is totally under the will of her parents to a rebellious woman, willing to do anything to save her love for Romeo. It is doubtful the Juliet the audience meets in Act I is the same girl who is willing to fake her death with a potion which will render her lifeless just to see Romeo again. She not only matures but takes on her problems with courage and certitude.
There are also several flat and static characters. I would include Lady Capulet, Lord Montague and Lady Montague among these. The audience knows little about them other than Lady Capulet is uncomfortable around her daughter and Lord Montague will build a statue for Juliet. Balthasar and Count Paris also take on flat and static characteristics. They seem to be simply a product of the plot as is the servingman with the party list in Act I. Certainly an argument could be made that the Prince is round and possibly even dynamic, but the audience just doesn't know enough about his character attributes. He is a ruler and is needed to drive the plot with his edicts about the death penalty and his banishment of Romeo.