Kate Hardcastle is the character with whom the audience sympathizes the most. The central plot revolves around her trying to find a husband who will be compatible with her rather than just one of the right social class. The other marriage and love plots in the play serve mainly as foils to the central plot. Constance is similar to Kate and her plot runs in parallel with Kate's; she takes on the typical "best friend" role in the play. Mrs. Hardcastle acts as the stock character of the "matrona" serving as an obstacle to Constance's romance. Tony Lumpkin is theantagonist. Hastings and Marlow play the role of suitors, but are depicted as far less interesting, determined, and clever than the two girls.

Kate is the most dynamic and well-rounded character in the play and the one most transformed over its course.  

While the characters tumble over each other in this play of mistaken instructions, mistaken behavior and mistaken identity, the real story centers around Kate Hardcastle.  Kate is determined to marry for love, and not for social standing or convenience.  She is the title character, and she 'conquers' Marlow's heart by fooling him into revealing his generous and unbiased nature.  She undergoes a change, from disliking him to truly respecting and loving him, and in that change she sees the importance of crossing the boundaries of class and society.  She manipulates the situation and she wins out in the end.  With the action centering around her, Kate is the protagonist.

The most important character in this excellent comedy by Goldsmith is Marlow. This is because he is the one and only character who is willing to make the decision to marry based on nothing except his emotions. When he "courts" Kate, whom he believes to be nothing more than a barmaid, he gradually comes to fall in love with her, and when pressed by her in Act V, declares that love, saying that he will marry her no matter what her connections and her lack of a dowry. Note what he says:

By heavens, madam, fortune was ever my smallest consideration. Your beauty at first caught my eye; for wh could see that without emotion? But every moment that I converse with you, steals in some new grace, heightens the picture, and gives it stronger expression. What at first seemed rustic plainness, now appears refined simplicity. What seemed forward assurance, now strikes me as the result of courageous innocence and conscious virtue.

There is of course an irony in this speech, as Marlow sees Kate for the dignified well-brought up lady that she actually is, yet what distinguishes Marlow from everybody else is that he is not swayed by money or by connections. An important theme in this play is marriage and the way that Goldsmith satirises it to be the social contract that it was in his day rather than anything to do with emotions. Note how reluctant Constantine is to marry without her jewels. By contrast, Marlow is willing to marry a barmaid because of his emotions alone, which makes him the most important character simply because he is so honest. In a play that is all about hypocrisy and appearances vs. reality, honesty is a virtue indeed.